advice是用 a 还是an 还有 E-mail advertisement E-cat

advice是用 a 还是an 还有 E-mail advertisement E-cat 是a E-mail还是an E-mail?为什么, E-mail前面是用a还是an 还是不可数? e-mail是不可数名词,为什么还有“an e-mail” advertisement是用a还是an what的a发音一样的a是哪个 a.wash b.cat c.E-mail an e-mail to a penfriend an e-mail adddress 还有一题.短文填词.Li Lie gets an E-mail f__1__Jaok Wilson.Jack is a she has an e-mail address.(划线部分提问)an e-mail address是划线部分 this is an e-mail对an e-mail提问 advice前面是加a还是an