Kindergarten Entrance Exam

This is a quiz going around on Facebook recently, which was part of a entrance exam of a kindergarten in Japan.
The time limit is 5 minutes. Not a trick question or anything, but very logical quiz.

Ar you smart enough to be a kindergarten student???

There are 4 students wearing either a Black or White Cap in a room where divided into two sections. The student A cannot see other students who is behind the divider, and B, C, D cannot see the student A neither. Students do not know what color cap themselves are wearing, and also they are not allowed to look behind to see the student who’s standing behind you. (i.e. Student B can only see the divider, and not allowed to see his own cap or student C or D.) All students are informed that there’s 4 students total, and there are 2 black and 2 white cap each, and asked to figure which color cap he/she is wearing
after a moment of silence, one of the students could tell which color cap s/he is wearing.
which student is the one and how could s/he tell?

4人の男の子が図のように部屋の中に隔離されています。この4人にはあらかじめ次のことを知らされています。部屋に入っているのは全部で4人であること。黒いキャップを被っている人は2人、白いキャップを被っているのが2人。そして自分が何色のキャップを被っているかは知らされておらず、自分で自分の頭のキャップを手にして見るのは駄目。またA君とB、C、D君との間は壁で仕切られて相手が見えない。全員後ろを振り向いて見ることも絶対だめ。さて、ここまでの条件をこの4人に話した上で、自分が何色のキャップを被っているかわかった人は声を出して答えてください、と部屋の外から先生が問いかけるのです。ここからが問題です。しばらくの沈黙があった後、自分のキャップの色を当てた少年がいます。それはA、B、C、D4人のうち誰で、その理由はなぜ?

Scroll down to my solution (should be right, but don’t’ know if this is the only answer or not….)

My answer is the Student C.
with the divider, and also they cannot look behind themselves, Student A and Student B will not be able to answer for sure.
Only possibility Student D can tell the answer is when student B and C are wearing the same color cap.
(because there’s only 2 caps of each color)
Since Student D did not call out the answer right a way, student C will know that the color of the cap the student B and himself (C) is wearing is different, thus Black.

any thoughts?

僕の出した答えは C君
壁で仕切られているためA君とB君は情報が少なすぎて(というか何の情報も入らないので)答えられない。
D君が答えられるとすれば、B君とC君は同じ色の帽子をかぶっている場合のみ。
C君は、D君がすぐに答えられない理由がB君と自分が別々の色の帽子をかぶっているからだと言うことに気がつけば自分が黒だということがわかる。

さて、どうでしょう?

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