I am Carrie.I highly appreciate your effort. I think the mistake maybe (D) "completed". It should be corrected "to complete". However, I am not sure about this grammatical point. I would like to see the anwser. Thanks in advance.
I'm with Clive on that. I can't see any error in the sentence. B can be substituted with 'where' or 'that' but it doesn't mean that 'when' is unacceptable here.