Ｉ．从A、B、C 三个选项中选择最佳答案。（每小题1分，共10分）
( ) 21. Seven __________ workers work in that factory.
A. thousand B. thousands
C. thousands of
( ) 22. — Where ________ the camel ________?
— Africa.
A. does; from B. is; come from
C. does; come from
( ) 23. — Does the lion eat grass?
— _________
