Question

which sentence includes a gerund?
walking three miles is an excellent form of daily exercise
singing lessons had been a dream of hers for years
we were hiking alongside the river last saturday
sarah was diving into the lake from the raft all afternoon

Explanation:

A gerund is a verb - ing form that functions as a noun. In the sentence "Walking three miles is an excellent form of daily exercise", "Walking" is a gerund. It is the subject of the sentence (acting as a noun). In "Singing lessons had been a dream of hers for years", "Singing" is an adjective modifying "lessons". In "We were hiking alongside the river last Saturday" and "Sarah was diving into the lake from the raft all afternoon", "hiking" and "diving" are part of the past continuous tense (verb forms, not acting as nouns).

Answer:

Walking three miles is an excellent form of daily exercise.