Choose the sentence that correctly adds an adverb clause to the sentence below.
“He realizes there must be a cobra in the room.”
a. He realizes there must be a cobra in the room because he sees a bowl of milk.
b. He realizes there must be a cobra which is deadly in the room.
c. He quickly realizes there must be a big cobra in the room.
d. He, the American, quickly realizes there must be a cobra in the room.