(1) Roller derby is a high contact extreme sport that began in the United States during the 1920s. (2) This sport takes place on a long oval track. (3) Participants earn points by skating past, or "lapping," members of the other team. (4) Roller derby is primarily played by women, and most skaters are amateurs who raise their own support in order to participate. (5) Many skaters wear fun costumes and adopt fake names to express their personalities. (6) Because many injuries can occur at roller derbies, emergency medical personnel are required to stay rinkside, and skaters must wear protective gear at all times.

Which of the following is an example of a compound-complex sentence?
A.
sentence 6
B.
sentence 5
C.
sentence 3
D.
sentence 1

A compound-complex sentence is formed by two independent clauses and a dependent one, at least. In sentence 6, the two independent clauses are the following:

1. emergency medical personnel are required to stay rinkside,

2. and skaters must wear protective gear at all times.

Notice that the clauses above are capable of expressing a complete thought even if they stand alone. That is what makes them independent. The second clause begins with a coordinating conjunction (and), which is used to connect independent clauses.

Also in sentence 6, we have a dependent clause:

3. Because many injuries can occur at roller derbies,

The clause above, if read alone, would not make sense. The subordinating conjunction (because) shows that more information is necessary for the clause to express a full thought.

As we can see, sentence 6 is a compound-complex sentence.