preposition
1
BAD : Don't forget to off the lights before you go out.
GOOD : Don't forget to turn off the lights before you go out.
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turn off/on (or switch off/on ) a light, television, electric kettle etc: 'Let's turn on the radio and listen to the news.'
2
BAD : The glass fell off of the table.
GOOD : The glass fell off the table.
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Off + sb/sth (WITHOUT of ): 'I wish he'd wipe that silly smile off his face.'