通读短文，掌握其大意，然后在各小题所给的三个选项中，选出一个最佳答案。

    Sam is my new classmate. He is 1 American boy. He is from New York. He is thirteen.

    Sam often gets up at about 6: 30 on2. And he often 3 a cup of tea, an egg and some bread for his breakfast. Then he goes to school at 7: 30 a.m. and gets there 4 8: 00 a.m. . They have four classes in the morning and two in the 5. At 3: 50 p.m. they play games. He studies hard and studies 6. He likes English and is good at it. He teaches us 7 and we teach him Chinese. He can speak a little Chinese now, but not 8 . Mike is his good friend. They go home together(一起). He does 9 homework at home, but sometimes at school. On Saturday and Sunday, he likes 10 football games on TV. He often goes to bed at about nine.

在“测量小灯泡的功率”实验中，小灯泡的额定电压为2.5V．

2016年12月，中共中央办公厅、国务院办公厅印发了《关于全面推行河长制的意见》。“河长制”，即由中国各级党政主要负责人担任“河长”，负责组织领导相应河湖的管理和保护工作。“河长制”工作的主要任务包括水资源管理保护、水域生态治理修复、水污染防治等六个方面。

结合材料，根据所学知识回答：

12－____＝7。