Q9 Answer
2 DIAMONDS
NORTH has a big hand - 22+HCP balanced or 20/21+ HCP unbalanced. If you have 0-6 HCPs your response is 2D (the waiting bid) Also you may have 8+ HCPs but no good bid (e.g. 4441 distribution.
Q19 Answer
3 NO TRUMPS
Your partner has opened and has 6 diamonds and lots of HCPs. You have 15 HCPs and all 4 suits have been bid so you should be in game. So should it be in diamonds or 3NT? 3NT is always better than a minor, so 3NT.
Q10 Answer
XX
You have 10+HCPs and no fit, so you XX. This means that you have 10+ HCPs and no fit.
The alternative is to bid 2C.
Q20 Answer
3NT
Your partner has cue bid 3D, saying that they have HCPs, as you have stoppers in diamonds and >16 HCPs, bid 3NT.