There is (an) "o" in the word "front".为什么括号里填an

There is （an） "s" in word "sun".解释这句话的意思和括号里为什么填“an"? There is only ( ) apple on the table.括号里应该填an还是one?为什么? There is___"o" in the word "front" 填a/an/the,1.There is ( )"x"in the word "box"2.( )Shanghai is There is an "s" in the word "bus".为什么用an there is an "h" in the word "house".为什么用"an"修饰"h" is there an old sofa in front of the wall? there is ____（a/an）“o” in this word. 填空：You're dropped ( )"s" in the word "necessary"括号里填 a 还是 an There is ____“u”in the word your.（填a或an） There is ____ s and ___u in the word 填a还是an? There is---- "s" in the word "snake"?请问横线上填a还是an