Got it right originally, second guessed myself in BR. Anyone else have this issue?

This section is making me not want to pursue law school :)

I am really confused by the "let's review" portion. The "Most before all" argument DOES say that:

A -m-> B --> C

Therefore, A -m-> C

But in the "let's review" part of this lesson it says that:

A -m-> B --> C yields no valid conclusions via the chain.

Can someone explain this please?