It was raining yesterday, so we ________ out.

The most common and grammatically correct way to complete the sentence is "didn't go" or "did not go". The full sentence reads: "It was raining yesterday, so we didn't go out." Here's why this is the correct choice: • Past tense: The sentence is about an event in the past ("yesterday"), so it requires a past tense verb. • Negative construction: To form a negative statement in the simple past tense, you use the auxiliary verb "did" followed by "not" and the base form of the main verb ("go"). • No double past tense: The auxiliary verb "did" already carries the past tense, so you do not need to use the past tense form of "go" (which is "went"). This is a common grammatical error.