题目

校园内的一棵大树在初夏阳光的照耀下所进行的生理活动有（    ） A．光合作用和呼吸作用                B．光合作用、呼吸作用和蒸腾作用 C．光合作用和蒸腾作用                D．呼吸作用和蒸腾作用 答案：B --- It’s difficult for the village children to cross the river for school. --- I think a bridge ________ over the river. A. should be built B. is being builtC. has been builtD. was built