Migrations take place on land，in water, or in the air． Some animals migrate only short （）．Other migrations cover thousands of miles or kilometers．
A.正确答案Cperiods
B.spans
C.distances
D.lengths
Migrations take place on land，in water, or in the air． Some animals migrate only short （）．Other migrations cover thousands of miles or kilometers．
Migrations take place on land，in water, or in the air． Some animals migrate only short （）．Other migrations cover thousands of miles or kilometers．
A.正确答案Cperiods
B.spans
C.distances
D.lengths
