Answer: c) Spontaneous recovery
Explanation:
Spontaneous recovery is the mechanism in which conditioned response that was gone or vanished earlier occurs again after some period of time .Instant re-emergence of any memory, phobia, fear, thought that was previously gone is faced after time delay .
According to the question, Mariah is experiencing spontaneous recovery in which is facing water fear again after time delay even when she took swimming course to get rid this fear.
Other options are incorrect because observation learning, extinction and generalization is not determine classical conditioning process.Thus, the correct option is option(c).