Which does the following sentence contain?

Walking by the river is our favorite pastime.

participle
infinitive as subject
gerund as subject
prepositional phrase as adjective

I'm confused with whether it is a participle (a verb acting as an adjective) or a prepositional phrase as an adjective.

In the sentence "Walking by the river is our favorite pastime," "Walking" is a gerund acting as the subject of the sentence. A gerund is a verb form that functions as a noun. In this case, "Walking" functions as the subject of the sentence, indicating that the act of walking by the river is the favorite pastime.

To determine which element the sentence contains, we need to analyze the grammatical structure of the sentence.

In the sentence "Walking by the river is our favorite pastime," the word "walking" is indeed a verb form, but it is not acting as an adjective. Instead, it is a present participle that functions as the subject of the sentence. Thus, the correct answer is "participle."

To identify this, you can recognize that the word "walking" is the present participle form of the verb "to walk." It is not modifying a noun, but rather functioning as the subject of the sentence. In this case, it acts as a gerund phrase (verbal noun phrase) that functions as the subject.

Therefore, the sentence contains a participle, specifically a present participle acting as the subject.

Neither.

Read up on gerunds.