You chose 3 Diamonds. This is correct. This is a pre-emptive bid - showing 6-10 points and a 7 card suit.

Usually there is no intervening bid from opposition unless they also have a similar hand to yours, or have a very strong hand and feel confident of getting at least 3 in their suit. If they have a good hand, but want their partner's input to decide what to bid, if they DOUBLE, this would be taken as a Takeout Double, and partner should reply to it unless there is an intervening bid.  But on this occasion, we are going to have them No Bid.

The partner of the pre-emptor knows that the opening bid was weak, so the rule is not to reply at all unless you, as response bidder have at least 13 points, and then to put your partner to game in his bid, even if you have very little in it.

Here is your partner's hand.

Spades            K,9,7,6,2
Hearts             A,7
Diamonds        6,5
Clubs              Q,10,8,4

42. What should you reply to your partner's pre-emptive bid of 3 Diamonds?

a. No Bid
b. 3 Spades
c. 5 Diamonds