Question

Choose the word or phrase that correctly completes the sentence.I​ __________ to bed two hours before it started raining.

Answer 1

I feel like this is conditional but I'm not too sure, I would go with A because it is a perfect past tense while D is simple past tense (I would use D is normal conversation though) 

D would be like answering a question "what did you do last night?" "I went to bed two hours before it started raining" 

A is like you're telling someone what you have already done using active voice "I had gone to bed two hours before it started raining" 

Take what you will from this, my friend. Sorry I can't be more of a help