To avoid vague pronouns and pronoun shifts, the writer should make sure that all pronouns

are subjective.
show ownership.
are first-person singular.
match their antecedents.

The correct answer is match their antecedents.

It is important for pronouns to match their antecedents in order to avoid confusion due to the pronouns being vague or shifting. For example:

She couldn't go out because her leg was hurting.

The pronoun her refers to the pronoun she, which is its antecedent, so it's clear who the sentence is talking about.

it translates into:

read the letter of your pen pal. write and answer 3 questions.