In bidding no-trump with three guarded suits, it does not matter which is unprotected.
It is just too weak for a no-trump, but at first glance seems too strong for a Spade.
My hand does not warrant a no-trump, because I have only two suits stopped.
A double of a no-trump is much safer than of a suit declaration.
If you are the leader at "no-trump," open your longest suit.
The dealer, Z, makes it no-trump and A leads for the first trick.
Z, the dealer, makes it no-trump, and A leads for the first trick.
Any overbid of an adversary shows strength; an overbid of a partner who has declared no-trump may show weakness.
A no-trump being thus eliminated, he, acting on the assurance given by the original call, may carry the suit to high figures.
(b) The two Spade bid should be used as a no-trump invitation with any hand not quite strong enough to justify a no-trump call.