Imagine if they were fractions, so 2:3 would be 2/3 and so on.
The question is asking if any of those equalities (like 2:3 = 3:2) are true.
A) 2/3 = 3/2
Multiply both sides by 6:
4 = 9
Not true.
B) 42/7 = 6/2
6 = 3
Not true.
C) 3/5 = 12/20
Multiply both sides by 20
12 = 12
True
D) 14/6 = 28/18
Multiply both sides by 18
42 = 28
Not true
The only true one is C.
Answer: C.