dokiyoki,
Choice A says:
"Stocks and portfolio investment failures have caused many concerned investors to move major accounts, such as 401-K and other retirement accounts."
The implication here (think parallelism!) is that there are two things that caused concerned investors to move major accounts: stock, and portfolio investment failures. However, "stocks" by themselves did not cause the investors to move accounts; stock failures did. As such, the meaning of A is nonsensical.
B) is wrong because it says "stocks investments and other..." If there were three things in this list, you would need a comma between stocks and investments. But that still wouldn't make sense. When we take "stocks investments" as a subject, it doesn't make any sense. So there is no way to make the subject correct here.
Your reasoning for D) is fine.
In E) we have "Portfolio investment failures, including stocks have caused." If we're trying to make "including stocks" part of the investment failures, we would need a comma after "stocks." As it is, it doesn't make any sense.
Hope that helps!
Brett