There is _ "e" in the world "eight"

There is _ "e" in the world "eight"
A.a B.an C.the

"e"不是元音字母吗？我觉得应该选B。正确答案给的是A。
谁给我讲解一下？谢谢。

there _(are\is) +some+不可数名词 There is There exists a doubt whether there is water on the Mars,_?Either you or I am wrong,-?附加疑问句???? there is （ ） over there There is ,there was, there were 造句 While there is life ,there is hope. there is a hero There is considerable ...... There is _____answer. No One Is There