Smaller pieces of rock from old, broken-up comets become
a. comets
c. meteoroids
b. meteorites
d. planetoids

c.meteoroids

Explanation:

Meteoroid is a piece of a comet or asteroid.

A meteoroid is a piece of matter, like stone or metal, that travels in space. Most meteoroids are no bigger than a pebble. Large meteoroids are believed to come from an asteroid belt. Some of the smaller meteoroids may have come from the Moon or Mars. If a meteoroid falls into Earth's atmosphere, it begins to warm and glow. This is called a meteor.

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