The students will put off the outing until next week, ________ t

The students will put off the outing until next week, ________ they won’t be so busy.
A、when
B、as
C、since
D、while
【正确答案】：A
【题目解析】：学生们将郊游推迟到下周,那个时候他们就都不怎么忙了。