LEARNING CENTER

D) None of the first 3 auctions guarantee a balanced hand.

D) -- A raise to 3NT (assuming it isn't conventional) shows a balanced hand (no singletons or voids).
In A), the 3NT bidder could have, say:

 KQ108  
 KJ1087  
 Q  
 AQ2.
 

In B), the 3NT bidder could have, say:

 3  
 KQ10  
 KQJ107  
 J1096.
 

In C), the 3NT bidder could have, say:

 K2  
 --  
 AKQJ10876  
 QJ3.
 

#3 is a perfect 2NT bid.

#1 is better suited for a raise (via a 2 or 2 cuebid)
#2 and #4 are not strong enough.

On Hands 1,2 and 4, South should be balanced.

On Hand 3, South could easily have something like:

2
 KQJ  
 KQJ1098  
 AK10.
 

With #1, A negative double is better.
With #3, South isn't strong enough for 3NT
With #4, South is unbalanced and should bid 2

2. 2NT on this auction shows 11-12 with a club stopper. Only hand 2 fits that description. With 1, you should bid 2. With hand 3, you should make a cuebid raise of hearts by bidding 3. On hand 4, you should pass, hoping partner balances with a takeout double. This is sometimes called a penalty pass or trap pass.