Choose the pair of ratios that form a proportion

A. 4/14, 6/21 B. 3/7, 4/8 C. 6/3, 12/8 D. 6/5, 5/4

cross multiply and see whether the two products are equal

for example,
3/7 ≠ 4/8 because 3*8 ≠ 7*4