The conditional tense is rarely tested on the SAT, and usually when it is, the answer jumps out at you because it just sounds weird.
An easy way to think of the conditional tense is as the “if” tense. It describes something that hasn’t happened but that could happen. Take a look:
1) If I had studied more, I would have done well on the test.
2) If the sun comes out, the ice will melt.
The first sentence describes something that didn’t happen but that could have happened had something else taken place in the past. The conditional tense has a formulaic way of describing this: If X had “Verb”-ed, then Y (some event or outcome). Or even more simply, “Had X “Verb”-ed, then Y”.
The first sentence is even more straightforward and describes an event that can happen in the future if another condition is met. This simple conditional tense doesn’t really come up on the SAT.
Anyhow, you probably get this, since it’s the basic English you’ve known for as long as you can remember. So the SAT isn’t going to test something that most students get right away. Instead, the conditional tense would be a larger part of a question and probably won’t be tested directly.
The answer is (C), since there is no room for a conjunction in the conditional tense. Remember, you need “Had X Verb-ed, then Y (some event). Therefore, you don’t need “although”. Of course many of you can just tell by reading the sentence that the “although” sounds really jarring. I know, you shouldn’t use your ear on the SAT Writing section. But there are some instances in which a word clearly doesn’t belong. In this specific case, you have more than your ear to guide you; you now know the conditional tense.