✔ Correct Answer: D. The call is busy, someone must be on another line.

The correct answer to the question “Choose the sentence which is grammatically correct: The call is going busy, someone have be on another telephone.” is The call is busy, someone must be on another line.. This question belongs to Grammar Concepts & Terms in English. Practice the related questions below to master this topic for your FPSC, PPSC and NTS tests.