Received a PM asking me to respond. This isn't a great question.

First, it uses the exact same opening in every single answer choice ("exercises,"). The real test does not do this.

Second, one of the major issues (apparently) being tested is whether the information is properly two generally separate pieces of information (meriting two independent clauses, as shown in the original sentence) or whether the information is properly connected, with the later info subordinate to the earlier info.

So which is it? From a logical standpoint, could the two pieces of info be separate? Sure. From a logical standpoint, could the second piece be subordinate to the first? Sure. If both interpretations are possible, we're supposed to go with the original meaning... but the original sentence is clearly wrong because there's no appropriate noun reference for the singular pronoun "it." Okay, so A can't be right.

B and C make the second piece of info subordinate. So they're apparently both wrong? (See below.)

D has two independent clauses... but connects those two independent clauses with only a comma, which is not allowed.

E changes the meaning unacceptably: E makes it seem that the fact that the dancers warm up then causes the routine (the warm-up) to reduce injury. But that's circular: the warm-up itself reduces injury; the warm-up doesn't cause the warm-up to reduce injury.

If we go just by grammar errors, then it has to be C because it doesn't contain any grammatical errors, and the others all do. But the real test wouldn't present a question to me in quite this way, for the two reasons I listed above.