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Common Mistakes and Confusing Words in English
Certain as an adjective is used when something is impossible to avoid or extremely likely to happen.
For example: "They were certain that they would pass their exams."
Curtain is a noun used to describe a piece of material that hangs across a window or opening to make a room or part of a room dark or private.
For example: "I draw the curtains as soon as it gets dark outside."