For each of the following situations, indicate whether the researcher has made a type I error, a type II error, or the correct decision.

a. The researcher rejected the null hypothesis when, in fact, the null hypothesis is false.

b. The researcher retained the null hypothesis when, in fact, the null hypothesis is false.

c. The researcher rejected the null hypothesis when, in fact, the null hypothesis is true.

d. The researcher rejected the null hypothesis when, in fact, the null hypothesis is false.