What is Hidden terminals problem?

What is Hidden terminals problem?
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Suppose that there are three mobile A, B, and C. The transmission range of A reaches B, but not  C. The transmission range of C reaches B, but not A. Finally the transmission range of B reaches  A and C.
A starts sending signal to B, C does not receive this transmission. C also wants to send data to B  and senses the medium. The medium appears to be free, the carrier sense fails. C also starts  sending data. It will create a collision at B. But A cannot detect this collision at B and continues  with its transmission. A is hidden for C and vice versa.
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Last Answer : Answer: C