27. When they …. in Shanghai, they .…

Question

amazed.
(A) arrive / will be
(B) will arrive / will be
(C) arrived / would be
(D) had arrived / were

i think it is not B and A
but between C and D...i don't know

Answer 1

This sentence depends upon the context. If they will arrive in the future, then A is correct. If they've already arrived in Shanghai, then D is correct.