Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?  Choose the correct choice from the following answers:	A) 15	B) 14	C) 17	D) 18	E) 19
In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.   15NSWER 15
<result>A</result>
Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?