人体与外界进行气体交换的系统是（ ）
A．消化系统
B．呼吸系统
C．循环系统
D．泌尿系统
答案：B
--- Could you tell me ?
--- Certainly. At 8 o’clock.
A．when will the train to Beijing leave
B．when the train to Beijing would leave
C．when the train to Beijing left
D．when the train to Beijing will leave
顶礼膜拜dǐnɡ lǐ mó bài
