问题补充:
Qian Xuesen tried many times he found the solution to the puzzle about space technology.
A. after
B. before
C. since
D. when
答案:
A. after
(答案→)B. before
C. since
D. when
解析:after在……之后;before在……之前;since自……以来;when当……时候。
句意:钱学森在他发现航天技术之前,他尝试了许多次。
时间:2021-08-14 18:36:18
Qian Xuesen tried many times he found the solution to the puzzle about space technology.
A. after
B. before
C. since
D. when
A. after
(答案→)B. before
C. since
D. when
解析:after在……之后;before在……之前;since自……以来;when当……时候。
句意:钱学森在他发现航天技术之前,他尝试了许多次。