9/20... 
I'm a bit confused about question Nr. 6:
Villain is unknown; it's the first time you're involved in a hand with him.
Preflop: Hero is SB with 4 :club:, A :spade:.
3 folds, Hero raises, BB 3-Bets, Hero calls.
Flop: (6 SB) 4 :diamond:, 6 :club:, 7
(2 players)
Hero checks, BB bets, Hero raises, BB calls.
Turn: (5 BB) 6
(2 players)
Hero bets, BB calls.
River: (7 BB) 5
(2 players)
Hero?
check/call (0 Points)
bet/call (2 Points)
check/fold (0 Points)
bet/fold (1 Points)
Your answer check/call (0 Points)
After just calling on the turn, your opponent will almost always be on an overpair, a pair on the flop or A-high. Against all of these, a bet is better than a check. In fact, he probably won't raise an overpair he has delayed anymore, but he would definitely bet it while he could still call another bet with A-high or his small pairs.
This of course isn't the best river card, but the FD busted and he could easily level himself into a call because he assumes that your range is polarized between FD and good made hands if you bet again on the river. Against an unknown opponent, you naturally want to see the showdown here, especially since this card is great for a bluff and his range will also be strongly polarized after a raise.
It is stated that villain is uknown, so we can rule out the advanced medium/high stakes tactics.
1. Opponents assumes Hero either has a made hand or a busted draw. Since 5 completes a lot of draws, villain will fold all his draws and raise only better hands. Hence I don't understand bet/call line to be the best as the article itself states that we villain won't raise overpairs and Hero is terribly behind against a whole range of overpairs. Therefore there is quite little chance to get called with any kind of unfinished draws, but on the other side we have to call a raise which will most likely come only from better hands?
2. FD which villain could had didn't complete and since it's already stated that villain will polarize our range between draws and strong made hands, a check would result in a bluff bet and if he has an overpair he will call anyway. We only lose against busted draws that don't bluff.
So, to draw the line - I'm wagering between bet/fold or check/call and would really like to hear some additional explanation of the bet/call line - against an uknown.