Question

Which sentence has an infinitive phrase?
The performers avoided the undertow by swimming to the middle.
The performers avoided the undertow, and they swam to the middle.
To swim, the performers avoided the undertow, and they swam to the middle.
The performers avoided the undertow and swam to the middle.

Answer 1

To swim, the performers avoided the undertow, and they swam to the middle. 

The specific element in the sentence that tells you that this is infinitive is the use of 'to' in front of swim. The sentence itself is garbage.