( )21.The Greens _____ China for seven years.
A. have come to B. have been to C. have come in D. have been in
( )22._____ the Great Green Wall, the land produces (生产出) more crops.
A. Thanks for B. Thanks to C. Thank to D. Thank for
( )23.It’s necessary for you _____ exercise every day.
A. taking B. to take C. take D. takes
( )24.-_____ you _____ your homework yet
-Yes, I _____ it ten minutes ago.
A. Did； do； finished B. Have； done； have finished
C. Have； done； finished D. Will； do； finish
( )25.Xi’an is a city with many places of interest and _____ tourists come here every year.
A. thousand of B. thousand C. thousands D. thousands of