Which of the options is the response variable? A. The number of adults.
B. The type of training exercises performed by each participant.
C. The size of the physiological blind spot.
D. The number of times an adult performed training exercises.

Question:  

The physiological blind spot refers to a very small zone of functional blindness in the eye where the optic nerve passes through the retina. We do not notice it because our nervous system compensates for it. Can eye training reduce the size of a person's physiological blind spot? Researchers recruited a representative sample of 10 adults with normal vision. Each participant performed training exereises with one eye for three weeks. The size of the physiological blind spot was measured (in degrees of visual angle squared) with a motion detection task both prior to training and again after the training was completed. Which of the options is the response variable?

A) The size of the physiological blind spot

B) The number of adults.

C) The type of training exercises performed by each participant.

D) The size of the physiological blind spot.

E) The number of times an adult performed training exercises.

The correct answer is A)

Explanation:

The response variable (when experimenting) is the variable or factor about which the researcher is concerned. It can also be (as the name entails) the variable which respond to changes in the experiment.  

The changes in the experiment is the training. The variable which the researcher is concerned about and which may or may not change with the introduction of training is the size of the physiological blind spot.

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you can't solve x because it is 2 linear equation and you only have one equation