A. on a second thought B. by second thoughts C. on second thoughts D. on the second thought
51. The foreign guests said that they were very happy ___ the great changes which had taken place in the village.(2001-19)
A. to B. for C. about D. by
52. Such problems ___ air, water, and noise pollutions are becoming more and more serious in some big cities.(2001-23)
A. like B. as C. of
D. about