Which of the following sentences contains an error in punctuation?

The sentence "The valley tends to be hot in the summer; snowy in the winter." contains an error in punctuation because the use of the semicolon is incorrect here. A semicolon is generally used to join two independent clauses that are closely related. In this case, "snowy in the winter" does not form an independent clause since it lacks a subject and a verb. A more appropriate punctuation mark would be a comma, which allows the sentence to flow better while still connecting the ideas.

The other sentences correctly use semicolons to link independent clauses or transitional phrases. In those, the clauses on either side of the semicolon could stand alone as complete sentences, which is a key requirement for their correct use.