Which sentence contains a structural error?

• A. The teacher explained the concept clearly, and the students understood.
• B. The teacher explained the concept clearly and the students understood.
• C. The teacher explaining the concept clearly; the students understood.
• D. The teacher clearly explained the concept, the students understood.

Answer: (C)

A complete sentence needs a subject and a finite verb to express a full thought, and punctuation like a semicolon is used to join two independent clauses. In the phrase The teacher explaining the concept clearly, explaing is a present participle forming a descriptive phrase, not a finite verb that can stand alone as its own clause. That left part isn’t an independent clause, so it can’t be paired with a semicolon to connect it to the next part. The second part, the students understood, is an independent clause, but the first part isn’t, which makes the whole construction structurally faulty. A correct version would pair two independent clauses, for example: The teacher explained the concept clearly, and the students understood. or The teacher, explaining the concept clearly, helped the students understand.