单项选择题
A．Many species have developed a habit of migration. B．Many species have become less sensitive to climate. C．Many new species have come into existence. D．Many species have moved further north.
A．They brought in bald eagles from Canada. B．They explored new ways to hatch baby bald eagles. C．They developed new types of feed for baby bald eagles. D．They found ways to speed up the reproduction of bald eagles.
A．those with vision defects B．astronomical observations C．the night blind D．optical experiments