I've been staring at answer choices A and D for a few minutes now. Is it just me or are they the exact same sentence?
Anyways, A (or D..) is the correct answer. B is incorrect because the 'too' after difficulties isn't correct. It should be 'to'.
As for C, the 'to' after are should be 'too'.
Too is like saying, "as well". It can also be used to say there's too much of something, etc.