Alphabet and numbers

Fill in the missing letter:
A, B, ___ D

• C
• E

G, H, ___ J

• E
• I

L, M, ___ O

• D
• N

What comes next?
1, 2, 1, 2, 1, 2, 1, _

• 1
• 2

What comes next?
1,1,2,2,1,1,2,2,1,_

• 1
• 2

What comes next?
4, 4, 4, 7, 7, 7, 4, 4, _

• 7
• 4

What comes next?
a, b, c, a, b, c, a, _

• a
• b
• c

What comes next?
9, 8, 7, 9, 8, 7, _

• 7
• 8
• 9

R, S, ___ U

• T
• L

X, Y, ___

• W
• Z