Which of these is an example of simple regression?

a. The race of a defendant and number of past arrests predicts the likelihood of a conviction.

b. The relationship between the strength of social support post-incarceration and recidivism.

c. The confidence of a witness predicts accuracy of their eyewitness testimony.

d. The number of eyewitnesses present plus the time of day a crime occurs predicts the time it takes to call the police.