Deal 9
 
  3NT
OL: 4
♠ A K
10 9 7
10 9 6 3
♣ K Q 8 5
 
 WEST  NORTH  EAST  SOUTH
1NT
pass3NTpasspass
pass

You are East. The bidding has been as shown.

Partner led the 4, won by South's 8.

South enters dummy with the ♠K and leads the 10.
What do you play?

When you have made your choice click NEXT .
♠ 2
4

♠ J 9 7 4 3
5 2
A 8 5
♣ 9 7 4
  ♠ 6
8

 

 
Deal 9
 
  3NT
OL: 4
♠ A K
10 9 7
10 9 6 3
♣ K Q 8 5
  Play the A.

You don't have much in your hand, but you do have the A, and you also have the responsibility to help West set up his suit.

So even though you don't know for sure how good that suit is, your plan of action should be to take the A and return a .

As you see, this will defeat the contract.
Had you played a low South would have pocketed that trick and added 4 ♣s and 3 ♠s to go with the he had already won.

 Deal 10 
♠ 8 5 2
A Q 6 4 3
7 4
♣ 10 6 3
♠ J 9 7 4 3
5 2
A 8 5
♣ 9 7 4
  ♠ Q 10 6
K J 8
K Q J 3
♣ A J 2