选择题
2012 AMC 8 Problem 9: Birds and Mammals
The Fort Worth Zoo has a number of two-legged birds and a number of four-legged mammals. On one visit to the zoo, Margie counted 200 heads and 522 legs. How many of the animals that Margie counted were two-legged birds?
A.
61
B.
122
C.
139
D.
150
E.
161