What should come in place of the question mark (?) in the following number series?
15 19 ? 27 31	Choices.
A) 21
B) 23
C) 20
D) 25
E) None of these
Explanation:   It increases by 4.   Answer:23
<result>B</result>
What should come in place of the question mark (?) in the following number series?
15 19 ? 27 31