As nobody here knows what is wrong with the machine, we send for an engineer to handle the problem．
A. should
B. must
C. can
D. would
网友回答
A. should
(答案→)B. must
C. can
D. would
解析：考查情态动词。should 应该，must 必须，can 能，would 会，句意：因为在这没有人知道这台机器怎么了，我们必须派人请一个工程师来处理这个问题。所以选B。