Final answer:
The infinitive in the sentence 'Jeremy's favorite activity is to swim.' is 'to swim.' It is being used as a subject complement, meaning it describes or renames the subject 'Jeremy’s favorite activity' in relation to the linking verb 'is.'
Step-by-step explanation:
In the sentence 'Jeremy's favorite activity is to swim.', the infinitive is the phrase 'to swim'. This involves the base form of the verb ('swim') preceded by 'to', which is the marker of the infinitive form. Unlike 'to' which can also function as a preposition, in this context, it's clear that 'to swim' is not indicating direction but is part of the infinitive form of the verb. The infinitive in this sentence is being used as a subject complement, which means it is renaming or describing the subject, 'Jeremy’s favorite activity'. It is not acting as an object, adverb, or adjective, but rather complements the linking verb 'is' by further explaining what the subject's favorite activity involves.
As context, there are other ways 'to' is used in English. 'To' can signal direction, for example, 'I am going to the pool.' 'Too' is often used to mean 'also' or 'excessively', such as in 'Do you like to swim too?' Lastly, 'two' is a number, as in the sentence 'I swim two times every week.'