A psychology professor conducts a small study to see if humor in text would affect students' memory for the sentences in the text. She had two groups of students read a large set of sentences, one group read humorous sentences while the other group read similar sentences without obvious humor in them. After the reading phase, both groups were tested for their memory of the sentences read. Identify the dependent variable and the independent variable in this research topic.
a. DV-Memory of sentences; IV-Presence/absence of humor
b. DV-Presence/absence of humor; IV-Sentences
c. DV-Presence/absence of humor; IV Memory of sentences
d. DV-Sentences; IV-Presence/absence of humor