In which of the following sentence is the nonessential clause?

a) The man leaning against the wall is from the zoo.
b) The snake that he is holding is not poisonous.
c) Its coloring, which is brown and green, allows it to hide in marshy areas.
d) The snake slithering behind the rock is actually harmless.

c) Its coloring, which is brown and green, allows it to hide in marshy areas.

The nonessential clause is found in sentence C: "Its coloring, which is brown and green, allows it to hide in marshy areas."

The nonessential clause in a sentence is a subordinate clause that provides additional information about the main clause but is not necessary for understanding the overall meaning of the sentence. To identify the nonessential clause, we need to look for a subordinate clause that can be removed without significantly changing the meaning of the sentence.

Let's analyze each option:

a) The man leaning against the wall is from the zoo.
- This sentence does not contain a nonessential clause. There are no subordinate clauses in this sentence.

b) The snake that he is holding is not poisonous.
- In this sentence, "that he is holding" is a relative clause that provides additional information about the snake. However, it is essential to understanding which snake is being referred to. Therefore, this is not the nonessential clause.

c) Its coloring, which is brown and green, allows it to hide in marshy areas.
- In this sentence, "which is brown and green" is a relative clause that provides additional information about the coloring of the subject. However, if we remove this clause, the sentence would still make sense and convey the main idea. Therefore, this is the nonessential clause.

d) The snake slithering behind the rock is actually harmless.
- This sentence does not contain a nonessential clause. Like option (a), there are no subordinate clauses in this sentence.

Therefore, option (c) is the sentence that contains a nonessential clause.