Which of these sentences contains a subordinate clause?

Responses
A The poem that I read in class is by Maya Angelou.The poem that I read in class is by Maya Angelou.
B The maple tree in the back yard grew to be quite tall.The maple tree in the back yard grew to be quite tall.
C Working the early morning shift can be very exhausting.Working the early morning shift can be very exhausting.
D The red cardinal stood out against the white snow and the black barn.

A The poem that I read in class is by Maya Angelou.