verb
1
DUBIOUS : I'm sorry that I won't be able to attend your wedding.
GOOD : I'm sorry that I won't be able to be at your wedding.
DUBIOUS : I'm afraid that I can't attend your party.
GOOD : I'm afraid that I can't make it to your party.
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Attend is used mainly in formal styles: 'All committee members are expected to attend the meeting.' In other styles use be at, come/go (to) or (informal) make it (to) : 'Apart from John and Sue, who else will be at the party?' 'Did you go to the match on Saturday?' 'We hope you can come but don't worry if you can't make it.'
2
BAD : It's very important to attend to all the classes.
GOOD : It's very important to attend all the classes.
BAD : I won't be able to attend at the meeting.
GOOD : I won't be able to attend the meeting.
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attend a meeting, class, school, etc (WITHOUT to or at )