The best transition to add at the beginning of the third sentence is the following:
C. In addition.
Considering that the sentence introduces information that follows and agrees with the previous sentence, ‘in addition’ is the best transition as it specifies that the sentence will add more reasons for volunteering.
Martin Luther King Jr. was influenced by Thoreau’s "Civil Disobedience" because it explained methods for nonviolent protest. Option C is correct.
Thoreau’s "Civil Disobedience" was a blueprint for methods of nonviolent protest.
Thoreau wrote Civil Disobedience in 1849, amidst slavery issues and the Mexican-American war. He wrote it right after being imprisoned in Concord, Massachusetts charged with refusing to pay his taxes.
Thoreau claimed in the "Civil Disobedience" that the government was not fair, and democracy only favored and protected the majority.
He was reluctantto pay his taxes as part of the Civil Disobedience, since the Mexican American war would give way to an expansion of slavery he desagreed with.
Thus, Thoreau was regarded to as the pioneer of nonviolent methods to protest against the government and that inspired Martin Luther King Jr.
included elements of mystery, superstition, symbolism, and the supernatural.
hope this helps:)