UPSC 2017 CDS II English Paper

The given sentence is a hypothetical sentence which refers to an impossible condition in the past and its probable result in the past. It is completely unreal, because it is now too late for the condition or its result to exist. Hence, in such conditions, past perfect is used in ‘if conditional’ and perfect conditional is used in ‘main clause’. Therefore, ‘had started’ is the right choice. Thus, option (b) is correct.