题目内容：
根据下列材料，回答题：One day the bell is ringing.__________ 1. When he wanted to begin the lesson, the headmaster came and asked him to go to the office. Mr. Black said to the students, "You can study math by yourselves, please.__________ 2. "
A moment later, Mr. Black came back. He saw Martin talking with his deskmate BoB．Mr. Black was angry.
" Stand up, Martin," said Mr. Black.__________ 3. "
"I'm reading math now," said Martin.
Suddenly Martin found it was a history book in his hand. Then he looked at Bob's hands. He was holding a math book.__________ 4. "I'm sorry, Mr. Black, Bob is holding a math book and I' m holding a history book.__________ 5."
从方框中找出能填人原文的句子，使短文意思完整。
第1空正确答案是（ ）
参考答案：
答案解析：