Choose the sentence with the grammatical error below.

Answer
A
Aristotle studied under Plato then later in his life he tutored Alexander the Great.

B
Some people consider a four-leaf clover a sign of good luck.

C
Before the invention of the printing press, monks copied books by hand.

D
A family with a skeleton in its closet is likely to be safeguarding unpleasant secrets, not old bones.

Which of those sentences is a run-on sentence?