Question

Which sentence is Vague pronouns
24a. When the car hit a tree, it made a terrible noise.
24b. The car made a terrible noise as it crashed into a tree.

Answer 1

In which one could "it" be referring to either the tree or the car?

In one of them, the reference is very clear; in the other, it's not.

Let us know what you think.

Answer 2

Which sentence is Vague pronouns?
25a. Air pollution normally increases along with population growth. This increasing pollution is a big problem for many cities.
25b. Air pollution normally increases along with population growth. This is a big problem for many cities.

Answer 3

How about 25b? "This" is used as a pronoun -- but to what does it refer? Pollution? Population growth?

In 25a, "this" is used as an adjective. This sentence has no pronouns.