题目

The other day，my friend Jane was invited to a 40th birthday party．The printed on the invitation was 7：30 pm．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 David were restless．0ther 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：there was still no food．And everyone was completely off their heads .  Jane and D left hungry and angry．     Their experience suggests tha13．已知f（x）是奇函数，且当x＞0时，f（x）=x2+2x，则当x＜0时，f（x）=-x2+2x．