4. Let $a , b$ be positive real numbers. Then ``$a > b > 1$'' is a \_\_\_\_ condition for ``$\log _ { 2 } a > \log _ { 2 } b > 0$''\\
(A) necessary and sufficient condition\\
(B) sufficient but not necessary condition\\
(C) necessary but not sufficient condition\\
(D) neither sufficient nor necessary condition\\