The relationship between cell phone use and the incidence of brain tumors is still unclear, this is because some studies show a causal relationship while others do not.

A) is still unclear, this is because some studies show
B) is still unclear; some studies show
C) are still unclear because some studies show
D) is still unclear because: some studies show
E) is still unclear; the reason is that some studies show

The OA is B. But I don't understand what's wrong with E.Though it is wordy it maintains the contrast between two sentence while B doesn't...