Answer:
The sentence "When we opened the door, a skunk ran into the house" is a complex sentence.
Step-by-step explanation:
The sentence is composed of two clauses.
"When we opened the door" is a dependent clause (also called a subordinate clause) that starts with a subordinating conjunction "when" and provides the time or condition for the action in the independent clause.
"a skunk ran into the house" is an independent clause that can stand alone as a sentence. It contains a subject ("a skunk") and a verb ("ran") and expresses a complete thought.
The two clauses are connected by the subordinating conjunction "when". This type of sentence structure when two clauses are combined is called a complex sentence.