Answer:
C) Use a comma to set off a phrase or clause at the beginning of a sentence.
Step-by-step explanation:
The sentence consists of a phrase "In the early morning hours" and an independent clause "everything is silent and peaceful.". Whenever a sentence begins with a phrase or a dependent clause, a comma should be placed after that phrase or clause. The correct version of the sentence is the following:
In the early morning hours, everything is silent and peaceful.
The other options are incorrect because the sentence does not list three or more items in a series (A), the sentence does not have two complete thoughts but one: "everything is silent and peaceful" (B), and the adjectives "silent" and "peaceful" do not require a comma because they are already separated by the conjunction "and".