请问这怎么翻译的,thanks怎么选择

题目

请问这怎么翻译的,thanks怎么选择
Had electronic computers not been invented, many problems of space flight ______ now. A. could not have been solved B. could not be solved C. must not be solved D. should not have been solved

答案

选A.could not have been solved,不可能已经被解决.
space flight的许多问题,是长年累月逐步解决的.而不是今天一天就都可以解决的,所以不选B.