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!