根据下面的对话情景,在每个空白处填上一个适当的句子,使对话的意思连贯、完整。
A: Environmental problems have become more and more serious.
B: Yes , I think so. Last weekend I planned to swim in Qingcheng River. When I got there, I was shocked by what I saw. .But now, it is full of rubbish, and there is no fish at all.
A: !And the air pollution is serious, too. How I miss the blue sky and the fresh air! ?
B: First, we' must take action from ourselves. .
A: I agree. Being volunteers really helps.
B: Then, we need to invite more people to join us.
A: Good idea! But how can we do that?
B: ?
A: Sounds good! Let's do that!