【正文】 s. Leavi ng the moon’s gravity was not as pai nful as l eavi ng the earth’s. But returni ng to the earth was very fri ghteni ng. We watched, am azed as fire 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 exci ting too,” I sai d. “N ow I know m uch m ore about gravi ty! Do you thi nk we coul d bi sit som e stars next tim e?” “O f course, ” he smi l ed, “ whi ch star woul d you li 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 aproaching the “bl ack hole”. We coul d see some fai nt l ights around what looked l ike an empty space. Li Yanping sai d, “ That empty hol e i s li ke a m outh always needing to be fed. Those li ghts are thins that are bei ng pul ed into ti me by the gravi ty of the hol e. ” We watched wi th interest and amazement at the lights whi ch seemed to be going fai nter and fainter round the edge of the bl ack hole. Just then the l ights on our spaceship went our the and the puter stoped worki ng. What was hapeni ng? I tried to turn the spaceship away from the hol e but i t would not move. Would it eat us too? Suddenly the spaceship jumped and began to move round the edge of trhe hole too. The gravity of the “bl ack the bil l, si r, pl ease fet i t. H enry: Fet i t? Wel … thank you very m uch. That39。 ㈢項(xiàng)目建設(shè)單位 ****農(nóng)業(yè)種植有限公司。t want anythi ng el se from you. H enry: (shocked) My dear, i s that your papa? Porti a: H e’s m y step father, and the dearest one that ever was. H enry: O h, m y dearest dear si r, I regret what I sai d. You have got a job open that I want. Ol iver: Nam e it. Henry: Soninl aw. O li ver: Wel , wel , wel l! But you’ve never had such a job before. H ow can i t be sure you can do i t successful y? H enry: Try m e… oh, do, I beg of you! Gi ve m e 30 or 40 years , and … O li ver: O h, wel, al l ri ght. N arrator: Are Porti a and H enry happy? There are not enough word i n the bi ggest di cti onary to descri be i t. Di d the peopl e of London have a good tim e wi th thi s bit of news? Yes. Portia’s stepfather took that bank note back to the Bank of Engl and and cashed it. The bank note was then usel es for m oney but was hi s weddi ng gift to the young coupl e. Yes, the bank note was worth m il li ons of dol ars, but not worth on tenthe as m uch as how H enry felt about Porti a . Uni t 4 H ow li fe began on the earth No one knows exactl y how the earth began, as i t happened so l ong ago. However, accordi ng to a wi del y accepted theory, the uni verse began wi th a “ Bi g Bang “ that threw m atter in al l directi ons. After that, atom s began to form and bing to create stars and other bodies. For several bil li on years after the “ Bi g Bang “, the earth was sti l just a cl oud of dust. What i t was to be e was uncertai n unti l between 4. 5 and 3. 8 bil li on years ago when the dust settl ed i nto a soli d gl obe. The earthenware becam e so vi ol ent that i t was not cl ear whether the shape woul d l ast or not. It expl oded l oudl y wi th fi re and rock. They were i n ti m e to produce carbon, ni trogen , water vapour and other gases , whi ch were to m ake the earth’s atm osphere. What i s even m ore i m prtant is that as the earth cool ed down, water began to appear on i ts surface. Water had al so appeared on other pl as l i ke Mars but, unl i ke the earth, i t had di sappeared l ater. It was not im medi atel y obvi ous that water was to be fundam ental to the developm ent of l i fe. What many sci enti sts bel ieve i s that the conti nued persence of water al l owed the earth to di sol ve harm ful gases and aci ds i nto the oceans and seas. Thi s produced a chai n reacti on, whi ch m ade i t possibl e for li fe to devel op. Many m il li ons of years later, the fi rst extrem el y sm al l pl ants began to appear on the surface of the water. They m ulti pl i ed and fil ed the oceans and seas wi th oxygen, whi ch encouraged the l ater devel opm ent of earl y shel l fi sh and al sorts of fi sh. N ext, green pl ants began to grow on l and. They were fol owed i n tim e by l and anim al s. Som e were i nsects. O thers, cal led am phi bi ans, were abl e to li ve on l and as wel l as i n the water. Later when the pl ants grew i nto forests, reptil es appeared for the fi rst ti m e. They produced young general ly by l ayi ng eggs. After that, som e huge anim al s, cal l ed di nosaurs, devel oped. They l ai d eggs too and exi sted on the earth for m ore than 140 m il li on years. H owever, 65 m il li on years ago the age of the di nosaurs ended. Why they suddenl y di sapeared sti l rem ai ns a m ystery. Thi s di sappearance made possi bl e thi ef ri se of m amm als on the earth. These anim als were different from al l ife forms i n the past, because they Gavi n bi rth to young baby anim al s and prodeced mi lk to feed them . Finnal y about 2. 6 mil li on years ago som e sm al l cel ver anim al s, now wi th hands and feet, apeared and spread al over the earth. Thus they have, i n thei r turn, be e the m ost i mportant anim als on the pl a. But they no they l ooki ng after the earth very wel l. They are putti ng too much carbon di oxi de i nto the atm osphere, whi ch prevenrs heat from escapi ng from the earth i nto space. As a result of thi s, m any sci enti sts beli eve the earth m ay b e too hot to l i ve on. So whether li fe wil l conti nue on the earth for mi l i ons of years to e wil l depend on whether thi s probl em can be sol ved. A vi si t to the m oon Last m onth I was l ucky engough to have 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 three ti mes on our journey and that the fi rst change woul d be the