Polar bears live mostly on _____ sea ice, which they use as _____ platform for hunting seals. [ ]

A. a; a

B. a; the

C. 不填; a

D. the; 不填

为病员稀释痰液作雾化吸入，药物首选：

A．卡那霉素

B．地塞米松

C．α-糜蛋白酶

D．氨茶碱

E．舒喘灵