¹ 20-22 HCP, balanced hand

South has:

♠ K 4 3
♥ A 6 3
♦ K J 5 4
♣ J 6 5

What is his bid?
A 3NT
B 4NT
C 6NT

A 3NT (2 votes)
This looks a bit passive, though this is far from a clear cut case. If North has 21 ‘good points’ or any 22 points, he will (much) more often than not make 12 tricks. In other words: 6NT will be a good contract in most cases.

B 4NT (56 votes)
4NT is the correct bid. If bid directly over partner’s 1NT/2NT-opening the 4NT bid is not Blackwood but 'quantitative', meaning: an invitation for a slam. South conveys this message to North: 'Partner, please pass if you have a minimum hand but bid 6NT if you have a maximum hand.' 

Having 20 points North will pass. Having 21 points and something extra (e.g. a five card suit or many tens) or any 22 points he will bid 6NT.

C 6NT (9 votes)
6NT is a bit too optimistic. If North has 20 points ‘only’, he will be defeated too often. True, he will make the slam now and then but not often enough too justify bidding it. South’s hand is just not good enough, all the more since it is 4-3-3-3.

PS 3♣, Puppet Stayman (which enquires after – amongst others – a five card suit in a major), was not given as a choice. Only use that convention if you have agreed with partner that afterwards you can still enquire after his strength (max or min) by bidding 4NT.

Not being able to use Puppet Stayman does not mean you will have to miss out on a 5-3 fit after jumping to 4NT. After all, if North accepts the slam invitation he can bid six in his five card suit, as a proposal to play there. If South does not like that trump suit he can still correct to 6NT.