11. All the apples ______ 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