How do you decide what to respond to? Also, what makes one a "top" discussion?

Oops I forgot to say about -- top discussion -- It's the discussions with maximum limit of response count. I guess the members whose discussion is in Top discussion -- are the members with many friends over there and there friends are helpful too .. not like my friends who just add and don't care much.

I used to respond to a discussion -- if the language is simple and easier to understand and the topic is of my interest and if I can see someone really need help and I can help him out. There are many ways by which I respond to a discussion ... Like I go through -- discussion started by my friends -- I usually don't find any discussion of my interest .. don't understand why people add me as friend request when they don't help ?? Anyways then if nothing happens .. then I look for discussion with no response and sometimes I find the disussion by search .. like I was responding to another discussion and happened to see yours and so I responded :)