Question

I'll give a medal.
Which word group best completes the sentence without introducing an inappropriate shift in tense?

He had been reading a book









A.

when the thunderstorm is starting.








B.

when the thunderstorm will start.








C.
when the thunderstorm starts.







D.
when the thunderstorm started.

Answer 1

Answer: D- When the thunderstorm started.
The original sentence "He had been reading a book" is of past tense.
A and C are in present tense while B is in future tense.
The only answer left is D which is also a past tense, therefore it doesn't introduce any inappropriate shift in tense.