选用所给句子完成对话。
A: Have you ever heard about a fund-raising event called Oxfam-trailwalker?
B: Yes. ____ 
A: Yes, it is. I am thinking of joining it. It’s a good chance to learn about working together.
B: ____ 
A: People over 18 years old. ____ 
B: It's a difficult walk but I’m really interested in it. Do you think I can join the walk?
A: ____  We can be in the same team.
B: Oh, ____ Let's find another two members.

生物界最基本的分类单位是____ ．在生物各类群之间，所处的共同分类等级越高，它们之间在形态结构和生理功能等特征上的相似程度____ ，表明它们的亲缘关系____ ．