Explanation

From my point of view, "C" is incorrect due to the operating systems being "incompatible". The passage advises having an operating system with some form of "variation" to protect a business from a virus, but this does not mean that it will have an "incompatible" operating system. Therefore, C is incorrect.

I think another reason C is wrong is because "not costly" is not specific enough. It could be not costly to implement the new system, but that could still be more costly than fixing the system after damages occur. In general, not costly is too subjective for us to make any conclusions about it.

B strengthens the argument by showing that there is a business case for the program the author advised. If the possible damage were minimal, and the possible costs were high to implement the program, it would make no sense to do it. B shows that the potential benefits are greater than the costs.