You need an X-ray.为什么X-ray前面是an?X不是元音字母啊?

关于X-ray,关为什么X-ray前面用an而不用a. Have you ever had an X ray? You must get an X-ray. 改为祈使句 Have you ever had an X-ray?When?Why? have you ever had an X -ray?如何翻译? "It is necessary for you to take an X-ray. X-ray怎么读? X-ray fluorescence是什么意思 X-ray grid X-ray什么意思 x-ray啥意思? x-ray in