The compound ratio of 5:7, 3:2 and 4:5?  Choose the correct answer.
A) 1 : 7	B) 6 : 5	C) 6 : 7	D) 4 : 7	E) 6 : 9

Rationale: "5 / 7 * 3 / 2 * 4 / 5 = 6 / 7 6 : 7 answer : c"
Answer: C