11, 10, ?, 100, 1001, 1000, 10001  Choose the correct option.
A) 1000  B) 121  C) 111  D) 101  E) 91
The pattern is - 1, × 10 + 1, - 1, × 10 + 1, - 1, × 10 + 1, ....   Answer : 101.
<result>D</result>
11, 10, ?, 100, 1001, 1000, 10001