题目

Mark needs to learn Chinese ______ his company is opening a branch in Beijing.   A. unless             B. until                C. although             D. since 答案：D下列的各项中与导管无关的一项是（　　）A．能输送水和无机盐B．是组成维管束结构的一部分C．能进行呼吸作用D．参与蒸腾作用