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
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
C
sea ice 海冰, 是固定结构，不用冠词；platform平台，是可数名词。