单项选择题

On the evening of his arrival in New York, Jimmy wanted to make a call to his mother. He found a telephone booth nearby and put some coins into a box in it and dialed 734-8681. At first the line was busy and then his call was put through. Jimmy was very glad to say "Hello!" to his mother. Just then came a sweet lady’s voice behind him.
"Are you through"
"Yes," Jimmy turned and said.
With a polite "Excuse me", the lady took up the receiver and dialed. Jimmy had to wait aside until, she put down the telephone.
After a while, Jimmy dialed again and heard his mother’s voice from far.
"What’s wrong with you Why did you ring just now"
"I myself don’t know why," Jimmy didn’t finish calling when a young man ran over and asked anxiously.
"Are you through"
"Yes."
With saying "OK!" the man quickly set the receiver to his ear and dialed. Jimmy didn’t know what to do. Just imagine how worried his mother was in London!

In the sentence "put some coins into a box in it" the word "it" refers to （）

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