"Everyone in our neighborhood mows their lawn on Saturday, and my street, as a result of that, is pretty." This construction:

has one error, a pronoun with no appropriate antecedent.

has two errors, a pronoun with no appropriate antecedent and a shift in tense.

*** has one error, an inappropriate combination of modifier and noun.

has one error, a lack of grammatical subject.

has two errors, a shift in number and a pronoun with no appropriate antecedent.

I agree.

No, sorry, that's not it.

The error focuses on the pronoun "their" ... what is its antecedent?

has one error, a pronoun with no appropriate antecedent.

has two errors, a pronoun with no appropriate antecedent and a shift in tense. Both verbs are in present tense, so this is not the correct answer.

*** has one error, an inappropriate combination of modifier and noun. The error has nothing to do with any modifier.

has one error, a lack of grammatical subject.
The subjects "everyone" and "street" are fine.

has two errors, a shift in number and a pronoun with no appropriate antecedent.

So ... which of the two left is the actual error?

Ooooh, okay! Thank you for your explanations to help me understand it! Is it the first one?

The correct answer is: "has one error, a pronoun with no appropriate antecedent."

To determine the error in this sentence, we need to analyze its structure and identify any grammatical issues. In this case, the error lies in the use of a pronoun without a clear antecedent.

Let's break down the sentence:
"Everyone in our neighborhood mows their lawn on Saturday, and my street, as a result of that, is pretty."

The initial part of the sentence states, "Everyone in our neighborhood mows their lawn on Saturday." The word "their" is a pronoun, used to refer back to the noun "everyone." However, the pronoun "their" does not have an explicit antecedent within the sentence. An appropriate correction would be to replace "their" with a specific noun, such as "his or her" or "each person's," to ensure clarity and agreement.

Here's an example of a corrected sentence: "Everyone in our neighborhood mows his or her lawn on Saturday, and as a result, my street is pretty."

By making this adjustment, we establish a clear antecedent for the pronoun and resolve the error.