Which is a run-on sentence?

AThey sing in a band, but they haven't had any shows yet.
BThey took the bus, it took a long time to get home.
CThey walk every evening, and it helps relax them.
DThey practice after school every day; it is very tiring.

Verified Answer :

BThey took the bus, it took a long time to get home. This is a run-on sentence, because it is not divided by the proper punctuation or conjunction, and when read aloud, we can even hear the error. All the other sentences are appropriately divided with a comma, but letter b shouldn't be partitioned by a comma.

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