When the alarm sounds, leave the building ___ once. A. at B. in C. on D. by Explanation: The idiom is "at once," meaning "immediately."
You should let us know ___ advance if you're vegetarian. A. in B. on C. by D. at Explanation: The idiom is in advance for prior notice.
He left the door open ___ purpose to let the cat in. A. on B. by C. for D. with Explanation: The idiom is used on purpose for deliberate action.
We discovered the mistake purely ___ chance. A. by B. on C. in D. with Explanation: The idiom is by chance for something accidental or unplanned.
Keep your passport close ___ hand when you travel. A. in B. on C. at D. by Explanation: The idiom is "at hand," meaning nearby and ready to use.
Only one nurse was ___ duty in the emergency ward. A. at B. in C. on D. under Explanation: The phrase is on duty for someone currently working.
Several coastal villages remain ___ risk during the storm season. A. in B. at C. on D. under Explanation: The phrase is at risk of being in danger.
She signed the contract ___ behalf of her father. A. on B. in C. at D. with Explanation: The phrase "on behalf of" is used when acting for someone else.
The fire is now ___ control, according to officials. A. in B. under C. with D. by Explanation: The expression is under control for a situation being managed successfully.
The buses here arrive every twelve minutes ___ average. A. in B. on C. at D. by Explanation: The idiom is on average for a typical rate or amount.