A short, hilarious joke

The geography teacher asked the students, where does this river go?

A student suddenly stood up and sang: The river flows eastward.

The teacher ignored him and then said, how many stars are there in the sky?

That classmate sang again: the stars in the sky can participate in Beidou.

The teacher is short of breath: get out!

Student: Just leave.

The teacher said helplessly, are you sick?

Student: You have everything I have!