Q8 Answer
DOUBLE or 2Diamonds
DBL. You cannot overcall 2H as you only have 4. You could say 2D but again you only have 4, with ten HCPs you could DBL saying you have 3 or 4 in the majors.
2D. If you only bid 1D with 4 diamonds then you would bid 2D. This system means that you occasionally bid clubs with only 2 cards.
Q18 Answer
Q28 Answer
PASS
When you pre-empt it is best not to bid again.
The only time you MUST bid again is when partner responds to the pre-empt with a change of suit, which is forcing. So PASS