(10 - 20) , (30 - 40) , (40 - 50) , (50 - 60)
Option:
Justification: This is the only pair in which the second number is twice the first one.

(10 - 20) , (30 - 40) , (40 - 50) , (50 - 60)
Justification: This is the only pair in which the second number is twice the first one.