Questions 11 to 13 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions. Now listen to the passage. It is unnecessary to reply to an invitation when _________.
A. the invitation bears the letters "R. S. V. P"
B. you are very busy.
C. a great many people are invited.
D. the hostess wants to invite others.
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