Which sentence is a complex sentence?

a. the dogs are barking.
b. when your father comes home, he will be upset.
c. the door was left open, and the cat escaped.
d. where is the cat now?

The correct sentences are B. and C.

Explanation:

By definition, a complex sentence contains two or more clauses. A clause is a grammatical unit: whenever a sentence contains a subject and a predicate, it is a clause. Examples of simple sentences are A. and D. In the case of B. and C., each of them contain two clauses. Sentence B.: clause 1 = "When you father( subject) comes home (predicate)"; clause 2 = "he (subject) will be upset (predicate)".