this pair of trousers is too short for the boy to ____ a. Put it on B. put on why not choose B? This question is for B. Is it because it's a sentence. There's no shortage of anything in the back

this pair of trousers is too short for the boy to ____ a. Put it on B. put on why not choose B? This question is for B. Is it because it's a sentence. There's no shortage of anything in the back

Put on verb preposition compound predicate must have an object, because the object is the pronoun it,
English is used to put it between put on