Hand C holds 9½ losers : 2 each in ♠ and ♣, 3 in ♦, and 2½ in ♥.

Hand D holds only 8 losers : 2 each in ♠ and ♥, 3 in ♦ and 1 in ♣.

Hand D has two additional advantages :

1. You have supporting Honours in clubs.
When you hold 2 or more Honours in the same suit, the suit (and the hand) is strengthened considerably, especially when the Honours are touching (AK, KQ) or only 1 space apart (AQ, KJ).

2. You have a 4-4 fit with Opener's diamond suit.
Although you probably won't play in diamonds, the 8 cards combined is likely to provide an extra trick in that suit.

3. You have a doubleton suit (in hearts).
If you play in NT this will not be an advantage.
But if Opener does not have the hearts covered you may well end up in a diamond contract, in which case your doubleton will be a positive.

With 10 points and 9+ losers, you must respond at the 1-level (or make a single raise of Opener's suit).  
But with 10 points and 8 losers you can respond at the 2-level.

Therefore with Hand C above you bid 1NT, but with Hand D you can confidently bid a new suit at the 2-level : 2♣ !