The correct answer is B: Only one signal can be received at a time. A disadvantage of FM compared with single sideband is that only one signal can be received at a time due to FM's capture effect. When two FM signals are on the same frequency, the stronger signal completely captures the receiver, and the weaker signal is not heard at all. With SSB, you can often hear both signals (though with interference). For amateur radio operators, this FM characteristic means you can't copy a weak signal if a stronger one is present, which can be a problem in crowded conditions or when trying to work weak DX.