Fill in the blank with the appropriate Modal from the options given below.
'If you smell gas, you _________ phone the emergency number.'
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → must
Complete sentence: If you smell gas, you must phone the emergency number. A gas leak is dangerous, so phoning the emergency number is necessary, not a choice.
| Option | Meaning and use | Example |
|---|---|---|
| (1) can | ability or permission. "You can phone" only says it is possible, which is too weak for a danger. | You can use my phone if yours is not working. |
| (2) must (answer) | Must expresses strong obligation or necessity: something that has to be done. It is the modal used in safety instructions and rules. | Passengers must fasten their seat belts during take-off. |
| (3) may | permission or possibility. It leaves the action to choice. | You may leave once you finish the test. |
| (4) should not | Should not is advice against doing something. Telling people not to call for help when they smell gas is the opposite of the right advice. | You should not touch a switch if you smell gas. |