Fill in the blank with the correct option: Note it down .......... you should…

Analysis and Solution

• The Sentence: "Note it down .......... you should forget it."

• The Grammar: The word "lest" is a conjunction that means "to avoid the risk of" or "for fear that." It is conventionally followed by the modal verb "should."

• Why D is correct: Using "lest" creates the grammatically correct idiomatic structure: "Note it down lest you should forget it," which implies writing it down to prevent the possibility of forgetting.