We _______ our dinner when it started raining last night.
We _______ our dinner when it started raining last night.
(A) had
(B) had had
(C) have had
(D) will have had
We had had our dinner when it started raining last night.
In this context, "had" is used as the Past Simple form of the verb "to have". The sentence describes a completed past action ("had our dinner") that was followed by another past action ("it started raining"). While the Past Continuous ("were having") is often used for an action in progress when interrupted, it is not an option here. Therefore, (B) is the best choice to indicate a sequence of events in the past.