The right answer is decida
The sentence:
Yo dudo que mucha gente decida a ir a un huesero.
is given in the subjunctive form. We use the subjunctive to express desires, doubts, the unknown, the abstract, and emotions. As in the indicative, the subjunctive mood includes the same verb tenses, including the perfect, the past, and the future.
So the verb decidir changes to decida for the first-person singular, the second -person singular (formal usted) and the third-person singular.
