Which sentence contains an idiom?

A. Martina’s heart sank when she woke up to lightning and pouring rain the morning of the picnic.

B. Jackson had a million different excuses for why he was unable to clean his room when asked to do so.

C. I was grateful for the outpouring of support I received from neighbors who helped me find my lost dog.

D. When the exam was finally over, it was great to have time for fun again after so much studying.