Why is C wrong?

Sorry I meant b in my initial post!

@ahlam, Happy to help. Let's look at (A), (B), and (C). (A) says, "Standardization of computer operating system software has increased computer compatibility among different businesses." (A) weakens the argument, as it gives a strong reason to keep the operating systems standardized, so we can get rid of it since we're looking to support the conclusion in the passage. (C) says, "It is not costly for a business to maintain incompatible computer operating systems." (C) doesn't support the conclusion because it doesn't matter. The operating systems discussed in the stimulus are still compatible with one another, so (C) is irrelevant. Thus, it's out. (B) says, "Correcting any damage resulting from an invasion by a computer virus program is more expensive than preventing the damage." (B) is important, as it informs us that preventing the damage (which means introducing the variations) is more cost-effective than correcting damage resulting from an invasion by a computer virus, so (B) does strengthen the argument for introducing the variations, as it says that it's economically better to do this. Thus, (B) supports the conclusion and is the correct answer choice. Hope this helps. Let us know if you have any more questions!

That was very helpful, thanks!

@ahlam, you're welcome!

Could it not be argued that C shows it is economically better to have the computer softwares with multiple variations? We are being told it is not costly to do so, and we already know that it eliminates the risk, so why wouldn't C strengthen the argument as well?

Nevermind, disregard my comment. I did not read the wording of answer choice C.