求求啦 “I have a headache ”.为什么headache前边要加一个a 而 “I have toothache”前边不加a?

求求啦 “I have a headache ”.为什么headache前边要加一个a 而 “I have toothache”前边不加a? 【小学6年级英语】重新排列句子：A：Oh,I am sorry to hear that.take good care of yourself.B:Hello,may I speak to Rose,please?C:thank you very much.D:This is Rose speaking.E:Hi,Rose.This is Lisa.I am ill.I have a cold.And I have a headac 是I have a news还是I have news谢谢啦啦 求求啦 求求啦, （ ）与...相比Tom,i have a happy familyplease啦 为什么说I have a bag 却不能说I am have a bag同志们,谢啦 英语翻译求求啦 求求啦,急用! 英语翻译求求你们啦! 求求好人啦! 求求你啦 2012年 求求啦 英语翻译求求你们啦~ 快,求求你们啦 求求你们了啦 求求你们啦 英语翻译求求你们啦