Which is a compound-complex sentence?

A) The dog began to bark at the visitor, and the cat ran under the chair.

B) The teacher had just started the math lesson when the fire alarm bell began to ring.

C) After they cleaned their rooms, the boys planned to go swimming, but it started to rain.

D) Both the boys and the girls were excited about going to the mountains and spending the night.

C). After they cleaned their rooms, the boys planned to go swimming, but it started to rain.

Explanation:

A compound-complex sentence as the name suggests brings the compound and complex sentences together that contains at least three minimum clauses which make it a complicated sentence that is used to convey longer thoughts. It carries at least two coordinate independent clauses with one dependent clause at least, joined with a coordinate and subordinate conjunction or a relative pronoun. According to the questions, option C seems to perfectly justify the above claim as it contains two independent clauses, 'the boys planned to go swimming' and 'it started to rain' and one dependent clause 'After they cleaned their rooms' joined with coordinating conjunction 'but'.

the answer is c

Explanation:

to be a compound complex sentence there needs to be two or more independent clauses and one or more dependent clauses!