The correct option is B are
In the given sentence, "The boys" is the subject.
'Boys' is a plural noun, and is in the third person point of view.
The verb that follows the subject must agree with it in terms of the person and number.
Option B: 'Are' is a plural verb that refers to a noun/pronoun in the third person. It agrees to the plural, third person noun 'boys'.
Hence B is correct.
Option A: 'Is' is a singular verb, it refers to a singular noun.
Option C: 'Am' refers to a singular, first person pronoun.
Option D: 'Was' refers to a singular noun.
They do not agree with the subject. Hence options A, C and D are incorrect.