The correct answer is A.
Zhèr yǒu sānge píngguǒ, nǐ yào nǎ yíge？
Tom：这儿 有 三个 苹果， 你 要 哪 一个？
There are three apples. Which one do you want?
Wǒ yào zhōngjiān de nà yíge.
Jack：我 要 中间 的 那 一个。
I want the one in the middle.
中间 (zhōngjiān) and 当中 (dāngzhōng) are very similar, both meaning “in the middle of” or “among.” In some cases, they are inter-changeable.
Zhèxiē júzi zhōngjiān yǒu yíge píngguǒ.
有 一个 苹果。
Zhèxiē júzi dāngzhōng yǒu yíge píngguǒ.
有 一个 苹果。
Both sentences mean “There is an apple among the heaps of oranges.
The difference between 中间 (zhōngjiān) and 当中 (dāngzhōng) is that 中间 (zhōngjiān) carries the meaning of “in the very center of something.” In the above conversation, three apples stand in line and the second apple is in the middle. So” 中间 (zhōngjiān)” is the proper choice. But “当中 (dāngzhōng)” can only be used to mean “among.”
Wǒ de péngyou dāngzhōng zhǐyǒu yíge nǚshēng.
1. 我 的 朋友
只有 一个 女生。
There is only one girl among my friends.
Zhōngjiān nàge nǚháir zuì piàoliang.
那个 女孩儿 最 漂亮。
The girl in the middle is the most beautiful one.