What is the participial phrase in the sentence below?
instructed with a teacher's care, the students increased their knowledge of the civil war.
a. increase their knowledge
b. the students increased
c. instructed with a teacher's care
d. of civil war

The participial phrase in the sentence is C. INSTRUCTED WITH A TEACHER'S CARE.

Participial phrase always starts with a participle. The participle may be present or past participle. Present participle ends with -ing. Past participles end with -d or -ed. 

In the above sentence, the participial phrase started with a past participle, Instructed. Always remember, participial phrases serve as adjectives in the sentence. It modifies students in the sentence.

By the end of 1970, the first Earth Day led to the creation of the United States Environmental Protection Agency and the passage of the Clean Air, Clean Water and Endangered Species Acts. “It was a gamble,” Senator Gaylord recalled, “but it worked.”

Explanation:

Have a horse-some day or night or whatever!

                    -nobody important