I saw _ UFO in the sky. 填a还是an?是根据U的读音填a 还是根据全称unidentified填an?

问题描述:

I saw _ UFO in the sky. 填a还是an?
是根据U的读音填a 还是根据全称unidentified填an?

a,a UFO
UFO是元音字母,辅音发音