The other day, my friend Jane was invited to a 40th birthday party. The time printed on the invitation was 7.30pm. Jane went off with her husband, expecting a merry evening of wine, food, and song.
By 9.45, everybody was having great fun, but no food had appeared. Jane and David were restless. Other guests began whispering that they, too, were starving. But no one wanted to leave, just in case some food was about to appear. By 11.00, there was still no food, and everyone was completely off their heads. Jane and David left hungry and angry.
Their experience suggests that the words on the printed invitations need to be made clearer. Everyone reads and understands the invitations differently. Most of us would agree that 6.30-8.30pm means drinks only, go out to dinner afterwards; 8.00pm or 8.30pm means possible dinner, but 9.30pm and any time thereafter means no food, eat beforehand, roll up late.
But this is not always the case. If asked to a students' party at 6.30pm, it is normal for guests not to appear before midnight, if at all, and no one cares. Being the first to arrive-looking eager-is social death. When my mother is asked to a party for 6.30, she likes to be there, if not on time, then no later than seven. My age group（late thirties） falls somewhere between the two, but because we still think we're young, we're probably closer to student-time than grown-up time.
The accepted custom at present is confusing(混乱的), sometimes annoying, and it often means you may go home hungry, but it does lend every party that precious element(成分) of surprise.
The underlined words "off their heads" probably mean______.

A．tired	B．crazy
C．curious	D．hopeless

Jane and David' s story is used to show that______ .

A．petty-goer8 usually get hungry at parties

B．party invitations can be confusing

C．people should ask for food at parties

D．birthday parties for middle-aged people are dull

For some young people, arriving on time for a students' party will probably be considered_______.

A．very difficult

B．particularly thoughtful

C．friendly and polite

D．socially unacceptable

According to the writer, people in their late thirties_______.

A．are likely to arrive late for a party

B．care little about the party time

C．haven' t really grown up yet

D．like surprises at parties

What is the general idea of the text?

A．It' s safe to arrive late just when food is served.

B．It' s wise to eat something before going to a party.

C．It' s important to follow social rules of party-going.

D．It' s necessary to read invitations carefully.