A：a-b-c
B：-a-b-c
C：-a+b-c
D：-a+b+c
为了帮助中国游客养成绿色旅游的习惯，政府制定了新规则。
The government has made new rules to help Chinese tourists to ____________________ of traveling in a green way.
蓄电池的电压为定值，使用此电源时，电流I
A: How old are you?（）
B: ___________________.
