The number 6 has exactly 4 positive factors and the number 9 has exactly 3 positive factors. How many numbers in the list 14, 21, 28,35, 42 have exactly 4 positive factors?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5
The positive factors of 14 are $1,2,7$, and 14 .

The positive factors of 21 are $1,3,7$, and 21 .

The positive factors of 28 are $1,2,4,7,14$, and 28 .

The positive factors of 35 are $1,5,7$, and 35 .

The positive factors of 42 are $1,2,3,6,7,14,21$, and 42 .

There are 3 numbers in the list (14, 21 and 35 ) that have exactly 4 positive factors.

ANSWER: (C)