Question

Which sentence is a run-on sentence?


A.
John Glenn was an astronaut; he was the first American to orbit Earth.


B.
Sally Ride was the first American woman in space, she was a member of a shuttle crew.


C.


When John Glenn traveled on the space shuttle Discovery, he was 77 years old.


D.
John Glenn first traveled into space in 1962, and he made his second space flight 36 years later.