In which sentence is the word swimming a gerund? The children were swimming in the shallow end of the pool. The swimming team members warmed up before the meet. Swimming is great cardiovascular exercise.

The correct answer is C. Swimming is great cardiovascular exercise.

In this sentence, "swimming" is a gerund. It functions as the subject of the sentence. In the first option, "swimming" is part of the verb phrase ("were swimming"). In the second option, "swimming" is part of the adjective and describes the team. Only in the final sentence does "swimming" function as a noun, or a gerund.