21. Human facial expressions differ from those of animals in the degree ____ they can be controlled on purpose.
A. with which B. to which C. of which D. for which
22. ---The job ____ by hand.
--Yes, a machine was unnecessary at all.
A. was done B. had been done C. could be done D. could have been done
23. The wet weather will continue tomorrow, when a cold front _____ to arrive.
A. is expected B. is expecting C. expects D. will be expected
