Memorising structure for all Primary triads

Question 1

Give the 4th degree (Sub-dominant of this note/scale) and then memories the combination. (If you are struggling then it is the 5th below)
C__
D__
E__

Answer 1

C___F
D___G
E___A

Question 2

Give the 4th degree (Sub-dominant of this note/scale) and then memorise the combination.
F___
G___
A___

Answer 2

F___B
G___C
A___D

Question 3

Give the 4th degree (Sub-dominant of this note/scale) and then memorise the combination.
B___

Answer 3

B___E