Toefl Test Grammar

[heisazadeh]

Please, explain. Why C is correct? Thanks in advance.
What is difference between three of every four and every four of three?

-------------------- migrating water birds in North America visit
the Gulf of Mexico's winter wetlands.
(A) Four of three every (B) Three every four
(C) Three of every four (D) Every four of three

[emsr2d2]

Duplicate post. Already replied to other one.