Why should you think about the points you want to make before you speak in group discussions?
a) so that you can avoid participating
b) so that you can communicate effectively
c) so that you can impress others
d) so that you can convince others that you are right

You should think about the points you want to make before you speak in group discussions b) so that you can communicate effectively  

Explanation:

Before speaking in a group discussion you have to be sure that you have clear and concise information, or that your comments and ideas are fully supported by a solid foundation, this way not only your idea can be easily and effectively convey but the discussion can generate a much more productive and beneficial outcome to all.