Hmm, I wasn't too pleased with this question when first looking upon it either.
However, your justification of B being wrong is entirely subjective, and not relative to psychological concepts.
What I've found with psych this year, is that you have to ignore your own logical assumptions for many questions. When considering answers, we MUST consider which psych concepts it is relating to, and deduct an answer based on what is proposed by these theories.
Taken directly from the 2010 Insight Solutions:
"B is correct. If studying two relatively similar pieces of information, it is best to allow time between the two so that each separate piece of information can be properly consolidated and not become confused."
This justification, i cannot argue with, as it is (sneakily) relative to consolidation theory, even though the main concept inferred by the question is Interference Theory.
C, is incorrect, as Interference theory is not about forming links between information. The two subjects (bio+psych) are going to be subject to interference NO MATTER WHAT, due to their similar nature.
I dont think you can voluntarily control interference
YES.
Sure, C may seem more LOGICAL, but B is PSYCHOLOGICALLY correct.