(b) That's not right. The issue raised by these facts is whether C caused harm to the console when, because of his negligent conduct, he drove into it.
It is important to notice that, in cases like this, the two incidents of negligent conduct that allegedly caused the harm happened independently of each other - and each could have caused the harm on its own. It is also important that the one incident happened before the other.
In such cases, the short answer is that, since the console was already damaged to the extent of needing replacement when C struck it, C's conduct did not cause any further harm. It is A's conduct which caused the harm to the console, and C's conduct did not in any way affect the extent of that harm.
Accordingly, A would be liable to B for the full cost of the replacement, but C would not be liable at all.