A handoff may be occurs when ______. (1) a mobile station changes its association from one base station to another during a call (2) people shut down his (her) cellphone. (3) the signal between the current base station and the mobile may have deteriorated to such an extent that the call is in danger of being dropped (4) a cell may have become overloaded, handling a large number of calls.

A. (1)(2)(3)

B. (1)(2)(3)(4)

C. (1)(2)(4)

D. (1)(3)(4)