Which one of the following statements is true for the base forms of verbs?

a. add "to" to the base form to create an adjective.
b. when the subject of a sentence is singular, add "–s" to the base form.
c. add "–ed" to irregular base forms to form the past participle.
d. do not use a base form with plural subjects.

The correct answer for the given question above would be option B. The statement that is true for the base forms of verbs is that, when the subject of a sentence is singular, add "-s" to the base form. For example, "He eats bananas everyday." The subject of the sentence is "he" which is singular. Therefore, the base form of the verb is added with an "-s" which is "eats".