Answer : 4. "91"
Explanation :

Answer: D) 91 Explanation: Here in the given numbers 91 is a Composite number. Since it has factors of 7 and 13 other than 1 and itself.   Composite Numbers : A composite number is a positive integer which is not prime (i.e., which has factors other than 1 and itself). Examples :: 4, 6, 8, 12, 14, 15, 18, 20, ...