Which of the following best describes the behavior of a gated channel?
(a) it stays open continuously when stimulated
(b) it opens more frequently in response to a given stimulus
(c) it opens more widely as the stimulus becomes stronger
(D) it remains closed if unstimulated

Option B ,  It opens more frequently in response to a given stimulus.

Explanation:

A gated channel is one which opens specifically to some kind of stimulus.  These stimulus could be a neurotransmission, a variation or change in the pressure, voltage, lights, chemical environment or any other physical parameter.  

For example  

Ligand gated ion channel which have receptors forming a membrane ion channel to allow passage of specific chemicals such as Na+, K+, Ca++, or Cl− only after the activation of receptor/channel complex.  

Hence, option B is correct