单选
21. Having ___ no-meat day would be a good way of encouraging ____low carbon life-style.
A. a; the B. a; a C. the; the D. the; a
22.—Can you give some advice on what I said just now?
—Sorry. My mind____.
A. is wandering B. was wandering
C. has wandered D. had wandered
23. Mr. Jones, a professor, _____for his excellent lectures, is popular with his students.
A. known B. knowing C. to be known D. having known
24. Of the two cameras, I would prefer _____ one, which is very easy for me to carry.
