In a certain sequence of numbers, a1, a2, a3, ..., an, the average (arithmetic mean) of the first m consecutive terms starting with a1 is m, for any positive integer m. If a1=1, what is a12?	Options
A) 100
B) 55
C) 23
D) 19
E) 1
As stated above, (a1+a2+a3......+a12)/12=12   therefore a1+a2+a3.......a12=144 (1)   using the same logic, we got a1+a2+a3..........+a11=121 (2)   (2)-(1) we got a12=23   23
<result>C</result>
In a certain sequence of numbers, a1, a2, a3, ..., an, the average (arithmetic mean) of the first m consecutive terms starting with a1 is m, for any positive integer m. If a1=1, what is a12?