When someone stands with their knees locked, they may feel dizzy, nauseous, and possibly faint due to a drop in blood pressure. this resulting drop in blood pressure would be classified as the
a
stimulus
b
sensor
c
control center
d
effector

C

Explanation:

The Stimulus is the fact of being with your knees locked. The sensors are the  nervous fibers that receive the sensation of feeling dizzy. The effectors are the muscles that respond to the stimulus.

hello there the answer is d

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.