'D' stands out as the most logical answer here ....Use of past perfect is very much needed ...Other difference being use of 'it' as Each of needs a singular pronoun...
Now as Zarrolou has pointed out that its not necessary to use past perfect if the sequence of the actions has been clearly demarcated using "BEFORE" ...As far as grammar says ... If the Past Perfect action did occur at a specific time, the Simple Past can be used instead of the Past Perfect when "before" or "after" is used in the sentence. The words "before" and "after" actually tell you what happens first, so the Past Perfect is optional. For this reason, both sentences below are correct.
Examples:
She had visited her Japanese relatives once in 1993 before she moved in with them in 1996.She visited her Japanese relatives once in 1993 before she moved in with them in 1996.On the other hand..
If the Past Perfect is not referring to an action at a specific time, Past Perfect is not optional. Compare the examples below. Here Past Perfect is referring to a general action rather than an action at a specific time. For this reason, Simple Past cannot be used.
Examples:
She never saw a bear before she moved to Alaska.
Not CorrectShe had never seen a bear before she moved to Alaska.
Correct