Which sentence is Vague pronoun
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.
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.
Not understanding which sentence is verb form and verb tense.
9a. The ancient Egyptians built pyramids as burial sites for their leaders.
9b. The ancient Egyptians have built pyramids as burial sites for their leaders.
Hereafter, please put up your own separate post....
Both of those are verb tenses.
"built" is simple past tense.
"have built" is a present perfect tense.
Check this site to see the sequence of tenses.
http://owl.english.purdue.edu/owl/resource/601/01/
The sentence with a vague pronoun is 25b: "Air pollution normally increases along with population growth. This is a big problem for many cities."
To identify the vague pronoun in this sentence, we need to determine what the pronoun "this" is referring to. In this case, "this" is used to refer to the previous statement "Air pollution normally increases along with population growth." However, the pronoun "this" by itself without any clear antecedent makes the sentence vague.
To improve the clarity of the sentence, we can replace the vague pronoun with a specific noun or phrase that directly refers to what is being discussed, such as "This increase in pollution" or "The increasing pollution caused by population growth."