We stayed at home because Mary wasn't very ______ on going out in the rain.

A．Because most black holes are so far away.
B．Because the gravity of a black hole is so strong that it sucks the light inward.
C．Because as the star’s gases burn, it stops giving off heat and light.
D．Because as a star cools, its outer layers pull in toward its center.

A．It becomes invisible.
B．It falls to Earth.
C．It burns up all of its gases.
D．It becomes brighter and easier to see.