下列物质中,属于纯净物的是
A:汽水
B:液氧
C:碘酒
D:食醋
— What did he _______ just now?— Sorry, I didn't catch his words. I_______ about something else.
保护动物的多样性要在遗传物质、____和生态环境三个层次上制定保护战略和采取保护措施.这些措施包括____保护、异地保护、法制教育和管理等.