In which sentence does the underlined gerund function as the object of a preposition?
a-in their free time, the children enjoyed drawing.
b-the child was dizzy from twirling.
c-singing was a favorite pastime.
d-the teacher encouraged reading.

First, you need to find prepositions in these sentences, because not all of them have them. There are no prepositions in C and D, which means we can eliminate those options. Now, you need to know what a gerund is. It is a type of a verb form that ends in -ing. Having that in mind, the object of a preposition is a gerund that follows a preposition. The answer cannot be A, because the preposition in is not followed by a gerund. This means that the correct answer is B. The child was dizzy from twirling.