Which sentence contains a dependent clause?

a. president madison always praised dolley for her keen political advice.

b. dooley was famous for her hospitality, serving as a hostess for many white house parties.

c. since james madison served as president from 1809 to 1817, dooley madison was one of the earliest first ladies.

d. james madison was new to the presidency, but dooley has already fulfilled some of the first lady’s duties.