What phraseology should be used to confirm altitude information for an aircraft in level flight?

Using the phrase "Verify at (altitude/flight level)" is the most appropriate choice for confirming altitude information for an aircraft in level flight. This specific phraseology provides clarity and precision, which is essential for effective communication in aviation. By including the actual altitude or flight level, it removes ambiguity and ensures that both the pilot and the controller are referring to the same altitude, facilitating safer operations.

In aviation communication, clear and standardized phraseology is crucial for preventing misunderstandings. The term "verify" signifies that the pilot should confirm the altitude they are currently flying at, and providing the specific altitude or flight level reinforces this request. This phrase also implies an acknowledgment that the altitude may need to be cross-checked against the altimeter setting and any previous instructions given.

Other options may lack the necessary specificity or standardized language that is preferred in aviation operations. While they may seem somewhat acceptable, they do not convey the same level of clarity and adherence to proper communication protocols as the chosen phrase does.