an 18-year-old high school student 为什么是an不是a

Jane is（）high school studentA.a 18-year-old B.a 18-years-old C.an 18-years-old D.an 18-year-old an 18-year-old high school student 为什么是an不是a an 18 years old,an 18-year-old有什么区别 a eleven-year-old还是an eleven-year-old 是a eight-year-old 还是an eight-year-old 英语翻译An 18 year old student at Chundkuli Girls' High School went missing,who was gang raped and murdered on Sept.7,1896 by eight Sinhala soldiers guarding the camp. The mountain is too high __this seventy year old man Mrs Green is a doctor of______and her daughter Ann is_____university sthdentA.50 years old;an 18-year-old B.50-year-old;an 18 years old C.50 years old;a 18-years-old D.50-years _____(a/an)1-year-old boy _____(a/an)8-year-old boy _____(a/an)11-year-old boy_____(a/an)13-year-old boy （a/an）18-year-old 18前面是an还是a in the 1927, the plane wasa. three-meter-high b.three meters higha为什么不对?急!an eight-year-old boy不是和a同理的吗？ The professional tennis player is______.A.an eighteen year old girl B.an eighteen-year-old girl C.an eighteen years old girlD.an eighteen-year-old girl 请问是an eleven-year-old boy还是an eleven-year old an eleven year old 和 an eleven-year-old用哪个?为什么 请简要说明理由1.The food in the restaurant is good ______ the price is too ______.A.and ; high B.but ; high C.but ; expensive D.because ; low4.I think a dog is a good pet for _________ child.A.a 6-year-old B.an 6-years-old C.a 6-year old D.a 6 1、be careful ____ _____ ____ (not play)with matches.2、Simon is an _____ boy .it means he is ____ A.18 years old;18 years old B .18-year-old;18 years old C.18 years old;18-year -old D.18-year-old;18-year-old an onehundred-year-old man用a还是an an eight-year-old一定要加an吗?