Does anyone have any tips on how to remember which words go with what group?

commenting to come back to when I am feeling like I can't do this... first one I got right and felt confident on ! It is possible!

What am I missing on question 4?

In the video they lay it out as A -m -> B, A-> C and then draw the conclusion that B<-s->C. Which is only the case if it is a two split mosts, right? A -m -> B A -m -> C then B <-s-> C.