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les ______ fell down from the tree were eaten up by the pigs. A. which B. / C. that D. they 12. I can tell you ______ he told me last week. A. all which B. all what C. that all D. all that 13. This is the biggest lab ______ we have ever built in our university. A. which B. what C. that D. where 14. Is oxygen the only gas ______ helps fire burn? A. that B. / C. which D. what 15. Air, ______ we breathe every day, is around us all the time. A. that B. / C. which D. it 16. This is the museum ______ we saw an exhibition the other day. A. that B. which C. where D. in that 17. This museum is ______ you visited the other day. A. that B. which C. where D. the one 18. This is the museum ______ you saw the other day. A. that B. where C. in which D. in that 19. It is the third time ______ late this month. A. that you arrived B. when you arrived C. that you’ve arrived D. when you’ve arrived 20. It was in 1969 ______ the American astronaut succeeded in landing on the moon. A. that B. which C. in which D. when 21. We often think of the days ______ we spent together o