Knowing the elements of a sentence and how sentences are structured can help you to get across your intended meanings in your writing and speaking. In sentence 10 the words knowing, writing, and speaking are all examples of A) gerunds. B) infinitives. C) participles. D) simple subjects.

In sentence 10 the words knowing, writing, and speaking are all examples of gerunds

it's gerunds actually

A)gerunds

Explanation:

The line ten of this excerpt shows the use of gerunds as different parts of the speech, gerunds can have varied uses and they always end in "ing" such as "knowing, writing, and speaking", these gerunds can work as subject of the sentence, the direct object, the subject complement, or an object of a preposition.