【正文】 a chance to make a tri p i nto space wi th m y fri end Li Yanpi ng, an astronom er. We vi si ted the m oon i n our spaceshi p! Before we l eave, Li Yanpi ng expl ai ned to m e that the forece of the gravi ty woul d change thre tim es on our journey and that the fi rst change woul d be the m ost powerful. Then we were off. As the rocket rose i nto the air, we were pushed back i nto our seats because we were tryi ng to escape the pul l of the earth?s gravi ty. It was so hard that we coul d not say anything to each other. Gradual l y the wei ght l essened and I was abl e to tal k to him. “ Why is the spaceshi p not fal li ng back to the earth? O n the earth if I fal l from a tree I wil l fal to ground. ” I asked. “ We are too far from the earth now to feel its pul , “ he expl ai ned, “ so we feel as i f there i s no gravi ty at al . When we get cl oser to the moon, we shal feel i ts gravity pul i ng us, but i t wi l not be as strong a pul l as the earth?s. “ I cheered up im m edi atel y and fl oated wei ghtl essl y around i n our spaceshi p cabi n watchi ng the earth be e smal er and the m oon l arger. When we got there, I wanted to expl ore imm edi atel y. “ Com e on, ” I sai d. “ If you are ri ght, my m ass wil l be l es than on the earth because the m oon i s sm al l er and I wi l be abl e to m ove more freely. I mi ght even grow tal er i f I stay here l ong enough. I shal certai nl y weigh l ess!” I l aughed and clim bed down the steps from the spaceshi p. But when I tri ed to step forward, I found I was carri ed twi ce as far as on the earth and fel over. “ O h dear, ” I cri ed, “ wal ki ng does ned a bit of practi ce now that gravi ty has changed. ” After a whi l e I got the hang of i t and we began to enjoy oursel ves. Leavi ng the m oon?s gravi ty was not as painful as l eavi ng the earth?s. But returni ng to the earth was very fri ghtening. We watched, am azed as fi re broke out on the outsi de of the spaceshi p as the earth?s gravi ty i ncreased. Agai n we were pushed back hard i nto our seats as we cam e back to l and. “ That was very exhausti ng but very exciti ng too, ” I sai d. “Now I know m uch m ore about gravi ty! Do you think we coul d bi sit som e stars next tim e?” “O f course, ” he smil ed, “ whi ch star woul d you l i ke to go to?” Caught by a bl ack hol e The spaceshi p warned Li Yanpi ng and m e to be ready as we were approachi ng the “bl ack hol e”. We coul d see some fai nt li ghts around what looked l ike an em pty space. Li Yanping sai d, “ That empty hol e i s li ke a m outh al ways needing to be fed. Those li ghts are thi ns that are bei ng pul l ed into tim e by the gravi ty of the hol e. ” We watched wi th i nterest and am azem ent at the l i ghts whi ch seem ed to be going fai nter and fai nter round the edge of the bl ack hole. Just then the l ights on our spaceshi p went our the and the puter stopped worki ng. What was hapeni ng? I tri ed to turn the spaceshi p away from the hol e but i t woul d not m ove. Woul d it eat us too? Suddenl y the spaceshi p jumped and began to move round the edge of trhe hol e too. The gravi ty of the “bl ack hole” was pul li ng us i nto i ts “m outh”. As the spaceshi p m oved round the bl ack hol e, I fel t rather si ck. My m outh went dry and I cl osed my eyes. Al the stori es about what happened when you were caught by the gravi ty of a “black hol e” seem to be true. But then the spaceshi p jumped agai n. Thi s tim e i t moved si deways and away from thi s edge of the “bl ack hol e”. Som eone watchi ng m e woul d have seen the spaceshi p fl yi ng l i ke a bi rd away from the “bl ack hol e”. But we fel t nothi ng. At l ast we were abl e to l ook around us. Lucki l y the puter had started worki ng agai n. We real i zed that we had di scovered som ethi ng new about “bl ack hol e”. If you go i nsi de the edge of a “bl ack hol e”, i t wi l “eat” you and there is no escape。 but i f you do not, you m ay have an opportunity to escape. H ow exci ti ng! Uni t 5 A tri p on “ The True North” Li Dai yu and her cousi n Liu Qi an were on a tri p to Canada to bi si t thei r cousi ns in Montreal on the Atl anti c coast. Rather than take the aeroplane al the way, they deci ded to fl y to Vancouver and then take the trai n west to east across Canada. The though that they coul d cros the whole conti nent was exci ting. Their fri end, Danny Li n, was wai ti ng at the ai rport. H e was goi ng to take them and thei r baggage to catch “The True N orth”, the cross Canada trai n. O n the way to the stati on, he chatted about thei r tri p. “You ?re goi ng to see som e great scenery. Goi ng eastward, you?l l pass m ountains and thousands of l akes and forests, as wel l as wi de ri vers and l arge ci ti es. Som e peopl e have the i dea that you can cros Canda i n l ess than fice days, but they fet the fact that Canada i s 5500 ki l om eters from coast to coast. H ere in Vancouver, you?re i n Canada?s warm est part. Peopl e say i t is Canada?s m ost beauti ful ci ty, surrounded by m ountai ns and the Paci fi c O cean. Ski ng i n the Rocky Mountai ns and sail i ng in the harbour m ake Vancouver one of Canada?s m ost popul ar citi es to li ve i n. Its popul ation i s i ncreasing rapi dl y. The coast north of Vancouver has some of the ol dest and m ost beauti ful forests i n the worl d. It is so wet there that the trees are extrem el y tal l, som e measuri ng over 90 m etres.” That afternoon aboard the trai n, the cousi ns setl ed down i n their seats. Earl ier that day, when they crossed the Rocky Mountai ns, they m anaged to catch si ght of some m ountai n goats and even a gri zl y bear and an eagl e. Thei r next stop was Cal gary, whi ch is fam ous for the Cal gary Stam pede. Cowboys from al over the worl d e to pete i n the Stam pede. Many of them have a gift for ri di ng wi l d horses and can wi n thousands of dol ars i n pri zes. After two days? travel , the girl s began to real i ze that Canada i s qui