D)
Lets break the given compound statements into atomic statements.
A : Good mobile phones.
B : Cheap mobile phones.
P :$(A\to \neg B) \iff (\neg A\vee \neg B)$
Q :$(B\to \neg A) \iff \big((\neg B\vee \neg A) \iff \neg A\vee \neg B)\big)$ (Disjunction is commutative),
Hence, $(P\iff Q)$ which means $(P\to Q)$ and $(Q \to P).$