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In Number sequece questions, you are given a long series of numbers. It is required to find out how many times a number satisfying conditions, specified in the questions, occurs.

Count each 1 in the following sequence of numbers that is immediately followed by 2, if 2 is not immediately followed by 3. How many such 1's are there ?
1  2  1  3  4  5  1  2  3  5  2  1  2  6  1  4  5  1  1  2  4  1  2  3  2  1  7  5  2  1  2  5

Option:
A. 2
B. 4
C. 5
D. 7
E. 9
Answer: B . 4

Justification:

1  2  1  3  4  5  1  2  3  5  2  1  2  6  1  4  5  1  1  2  4  1  2  3  2  1  7  5  2  1  2  5

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