Which of the following is ironic?

A.
A woman washes her car. Right after, it starts to rain.
B.
Someone writes a post on social media, arguing that social media is useless.
C.
A student has studied very hard for a test. When the test begins, he realizes he forgot to bring a pen.

C. A student has studied very hard for a test. When the test begins, he realizes he forgot to bring a pen.