Dear Mary:
It is my honor to receive your invitation. I am very glad to participate in
your birthday party. But I am sorry to tell you that I can't attend. I have to look after my grandmother instead of my parents. My grandmother is sick in bed. My parents go for a business travel and will not return until next week.What's more, the English exam is approaching.So I can't attend it. I am very sorry for this. Thank you for your invitation very much.
Yours
xxx
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