用不定冠词a或an填空,不需要的填"/".

用不定冠词a或an填空,不需要的填"/".
1、This is _____ pen.
2、That is _____ English map.
3、Is this _____ orange?
4、Is isn't _____ orange,It’s red.
5、_____ “e” is in “ruler”.
6、_____ “m” is in “map”.
7、The quilt is _____ white.
8、Is it _____ UFO in the sky?
9、The is _____ orange ball.
10、_____ “u” is in “you”.
（说一下解题思路,还有遇到这种题型,该用什么方法,）