Which of the Following Constitutes Consideration

Which of the following constitutes consideration?

A) Sherri does something she is not already legally obligated to do.
B) Sherri promises to do something she was not already obligated to do.
C) Sherri refrains from doing something she legally could have done.
D) Sherri promises to refrain from doing something she legally could have done.
E) All of the above.