1,11,21,_ what comes in the next series.
Choose the correct choice from the following answers:
A) 1 B) 11 C) 21 D) 31 E) 41
1+10= 
<gadget id="calculator">1+10</gadget>
<output>11</output>
11   11+10= 
<gadget id="calculator">11+10</gadget>
<output>21</output>
21   21+10= 
<gadget id="calculator">21+10</gadget>
<output>31</output>
31   ANSWER:31
<result>D</result>
1,11,21,_ what comes in the next series.