Marienka from Kosice, Slovakia sent in the answers for the dominoes to finish the patterns.

0 0 0 0 : 0 0
1 2 3 4 : 5 6

6 5 4 3 : 2 1
6 5 4 3 : 2 1

6 5 4 3 : 2 1
5 4 3 2 : 1 0

Bora from Irmak Primary School, Turkey used some excellent words to describe the patterns.

1st row: 5 and 6, because they are in decreasing order.
2nd row: 2-2 and 1-1, again in decreasing order, this time in doubles.
3rd row: 2-1 and 1-0, again in decreasing order, but both parts are full, upper part goes from 6 to 1, lower from 5 to 0.