雨が降りそうですから、出かけ___ほうがいいです。 (It looks like rain, so you had better not go out.)

Answer and explanation

Correct answer: B. ない

ない-form plus ほうがいい means had better not.
Answer: ない.
Why not the others: た: た would suggest it is better to go out. て: て cannot join ほうがいい. ます: ます cannot join ほうがいい.

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