题目

— Excuse me, which is the way to the museum?— Sorry, I don't know. This is my time here. A . first B . second C . two D . one 答案：A直接参与体内细胞与外界环境之间气体交换的系统是 [     ]A．循环系统和消化系统B．消化系统和呼吸系统C．循环系统和呼吸系统D．呼吸系统和泌尿系统