The increase in the threshold of a receptor when a series of stimuli of subthreshold intensity are applied in succession is called: (A) Adaptation, (B) Accomodation, (C) Initiation, (D) Resistance
Answer is B. Accommodation - Slow rising subthreshold stimulus failing to produce action potential even when the normal threshold levels are reached. 
This occurs because of inactivation of voltage-gated Na+ channels. 
Adaptation- Persistent application of suprathreshold stimulus fails to generate repetitive firing.