单项选择题
A．stopped migrating B．continued migrating C．began migrating again D．migrated south and stay there
A．birds should migrate in the middle of the winter B．longer days cause changes in the bodies of birds C．seasonal changes in the length of days do not affect migration D．increasing daylight increases the distance of migration
A．there was not enough food there in the winter B．there were too many birds C．there were too many glaciers D．there was too much daylight