Bidding with Larry!
Hand #1001 North is the dealer, NS Vul, IMP's. You're playing Standard American - Not 2/1. You are South holding: 
A743
32
KQ10
KQJ10
*3C=Artificial, 4th Suit Game Forcing
The double would tend to suggest spade lead (dummy's suit)
Incidentally, I actually prefer an immediate 2C response to 1H, but this is how the problem was presented.
A743 32 KQ10 KQJ10| West | North | East | South |
|---|---|---|---|
| 1 | Pass | 1 | |
| Pass | 2 | Pass | 3* |
| Pass | 3NT | Pass | Pass |
| Dbl | Pass | Pass | ? |
The double would tend to suggest spade lead (dummy's suit)
Incidentally, I actually prefer an immediate 2C response to 1H, but this is how the problem was presented.