Most and Some Logic Problems

[KristenG491]

Quick question I am getting tripped up on my some and most inferences after doing a drill in the LR book. For formal logic it says
Some + Some = (maybe) but can't really infer anything
Most + Some = (maybe but can't really infer anything
Most + Most = can infer a "some" relationship there

Now I was practicing the mini drills and got two probs that were supposed to be simple wrong.
1. Some cars are sedans and some cars are red.
(A) Most cars that are sedans are red.
(B) Some things that are red are cars.
(C) None of the above

The drill ask for what must be true (and in LSAT Q's I'm typically good at this) but I ended up choosing C because while I thought B was an answer in the LR book it says we can't infer anything! So, how can I choose what must be true if that makes sense?

4. Many dogs weigh more than 20 pounds and many dogs are difficult to train.
(A) Most dogs that weigh more than 20 pounds are difficult to train.
(B) Some dogs that are difficult to train weigh more than 20 pounds.
(C) None of the above.

The answer is C but I thought it was B. Like I mentioned before, I came up with this answer from the notes explaining most and some relationships