A expresses absolute necessity, while C expresses a condition.
Think of it this way: the government imposes a bridge tax. Is it a required measure to fix a problem? No, it's not an absolute requirement, it just helps raise money. If the town decides to devote 100k to organizing a new festival, is that a measure that fixes an issue? This is why A is out, IMHO. Some measures are not taken to solve problems, but for other purposes.
Now, if you have to raise taxes because public debt is out of control, it's a measure required to fix a problem. You have to do it, because it's the only way to raise money...
I hope this makes it a bit more clear...