第一节 单项填空(共15小题;每小题1分,满分15分)
从A、B、C、D四个选项中,选出可以填人空白处的最佳选项。
21. Long ago, man used
to ______ with his hands but now man is used to ______ with machines, and
sometimes a robot is used to ___ instead of people.
A. work, working, work
B. work, working, working
C. working, work,
working
D. working, work, work