OG 10 Q 204
The Qs is: In recent years cattle breeders have increasingly used crossbreeding, and partly because crossbreeding is said to provide hybrid vigor.
[D]:In recent years cattle breeders have increasingly used crossbreeding, partly because certain characteristics should be acquired by their steers and partly because crossbreeding is said to provide hybrid vigor.
Well, in my experience in any given SC question the correct answer is correct for at least two reasons. You may want to test both if you can spot what are the two errors in the sentence in the question stem. Also, when you read the question you need to understand what the writer is trying to say. Normally I imagine the writer to be a non-native speaker and I feel he wants to say something but does not know how to express his/her thought. So, I am only helping him/her frame the sentence properly. But that is my imagination. You can have something of your own.
In the given example parallelism might prompt you to pick C but that is a trap which the GMAC has designed for you. If you get it too easily you should know that may be you are missing something else and force yourself to read all the options.
Always remember to read each option. If you can spot an error right away (even if you have read it half way) then discard. Else, if the first pass of reading makes you feel it could be the right answer DO NOT jump for it, just keep it aside. Be patient and read the rest of the options. If none of the rest make any sense then go for the answer you picked first. But do remember to replace the answer option in the Qs stem and see if the entire sentence makes more sense.