Ptarmigan keep warm in the winter by _____

C

- Hướng dẫn giải

Phương pháp giải:

Giải chi tiết:

Đáp án là C. Ý trong bài: One way to do this is to find a sheltered roost. Solitary roosters shelter in dense vegetation or enter a cavity - horned larks dig holes in the ground and ptarmigan burrow into snow banks - but the effect of sheltering is magnified by several birds huddling together in the roosts, as wrens, swifts, brown creepers, bluebirds, and anis do. Body contact reduces the surface area exposed to the cold air, so the birds keep each other warm.