目前许多地区提出“绿色旅游”口号，主要是针对（   ）

    Mary is a student. She enjoys ____(run). Every morning, she starts to run near her home____ (介词) six o'clock. She also ____ (like) ball games. After school, she ____ (join) her classmates to play basketball. She ____ (eat) well too. She has three ____ (meal) at school. Her favourite food is ____(dumpling). But the dining hall is small with only ten ____ (table). The students are always ____(wait) there. Now it's time for dinner. Mary is ____ (walk) to the dining hall.

在硝酸银、硝酸铜的混合溶液中加入一定量锌粉，反应停止后过滤，滤液仍为蓝色，有关判断正确的是（　　）