how long have you been studying为什么后面要加ing

how long have you been studying为什么后面要加ing how long have you been studing english?为什么been后面是动词ing ,不是应该 How long have you been studying English? How long have you been studying? How long have you lived here?中的How long后面为什么要加have HOW long have you been studying english 怎么回答 How long have you been dancing today?为什么要加been!而T "How long have you been How long have you been 为什么加suffering from a headache不用suffer How long have you been living in China?为什么要用been,living是延续性动 how long have you been in china中为什么要用have呢? How long have you been skating?