<p>Almost all animals [that hibernate] prepare for [it] during summer [by eating] large amounts of food, [which they convert] to thick layers of fat. </p>
<p>Why is [it] an error?</p>
<p>“it” is unclear. Should be replaced by a noun like “hibernation”.</p>
<p>(it) does not have a clear antecedent. We know “it” refers to hibernation, however that’s not really stated.</p>
<p>Thanks. In general, is it possible for the antecedent of a pronoun to be in a relative clause/prep. phrase, or is that grammatically incorrect?</p>
<p>^Sure as long as it’s clear as to what the antecedent is. Obviously a pronoun cannot have the antecedent of a verb.</p>