The committee ____ decided on the new policy.

The subject 'The committee' is a collective noun, which refers to a group acting as a single unit. When a collective noun functions as a unit, it takes a singular verb. In this sentence, the committee is making a decision together, so the verb should be singular. 'Has' is the correct singular present-tense verb. 'Have' is plural and would only be used if the members were acting individually. 'Had' is past tense and does not match the present context. 'Having' is a participle and cannot serve as the main verb in this sentence. Therefore, 'has' is the correct choice.