In the following question, out of the four alternatives, select the alternative which is the best substitute of the phrase.
An involuntary action under a stimulus is described as a

Options

A. complex
B. reflex
C. reflection
D. response

Answer

B

Explanation

reflex (N.) : an action/a movement of your body that happens naturally in response to something and that you cannot control. complex (Adj.) : complicated reflection (N.) : a sign that shows the state or nature of something: an image in a mirror response (N.) : a spoken/written answer, a reaction to something that has happened or been said.