She still remermbers the days _____ she spent in the countryside.
A. while
B. that
C. when
D. during which
Helen was much kinder to her youngest child than she was to the others, _____, of course, made the others unhappy.
A. which
B. that
C. what
D. who
When people talk about the cities of U.S., the first _____ comes into mind is New York.
A. city
B. of them
C. one
D. that
The book was written in 1946,_____ the education system has witnessed great changes.
A. when
B. during which
C. since when
D. since then