Question

Which contains a sentence error?
Cold watermelon on a hot summer day is the best thing, a glass of iced tea is refreshing too.
Cold watermelon on a hot summer day is the best thing; a glass of iced tea is refreshing too.
Cold watermelon on a hot summer day is the best thing. A glass of iced tea is refreshing too.
Cold watermelon on a hot summer day is the best thing, but a glass of iced tea is refreshing too.

Answer 1

The first sentence is incorrect, as it has two complete sentences separated by a comma but with no connecting word between them