In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series.
21, 24, 19, (29), 17, 28, (15), 30

Given series 21, 24, 19, (29), 17, 28, (15), 30

from the two series is going on 

  fist is 21 , 19, 17 ,( 15) 

21-19= 2, 19-17= 2, 17-15= 2

the pattern is going dereaseing -2 to next number is going on 

second is  24 , (29), 28, 30

the above series is follow add +2 number in each next series 

   24, 26, 28, 30 

then the fist bracketed number (from left) is incorrect and second bracketed number (from left) is correct.

therefore Option (C) Ans