A 正确,another 另一个. 修饰可数名词单数
other 另外一些.
the other两者中另一个为什么不用other.other 修饰复数名词 、 或不可数名词， 如 other people 另外一些人 other water 另外一些水the other 可修饰单数名词（两者中另一)， 或名词复数I have two brothers, one is a teacher ,the other is a soldier There are 45 students in my class , six are girls, the others (= the other students) are boys.