Gaby lists the numbers $3,4,5,6,7,8$, and 9 . In her list, the ratio of the number of prime numbers to the number of composite numbers is
(A) $3: 4$
(B) $5: 2$
(C) $2: 5$
(D) $3: 7$
(E) $1: 6$
From the list $3,4,5,6,7,8,9$, only 3,5 and 7 are prime numbers.

The numbers $4,6,8$, and 9 are composite numbers.

The ratio of the number of prime numbers to the number of composite numbers is $3: 4$.