(focus on, keep... free from...) the scientists focused on keeping the atmosphere clean and free from pollution.

科学家们把精力集中在保持大气清洁和免受污染上。

youdao

(focus on, keep... free from...) the scientists focused on keeping the atmosphere clean and free from pollution.

科学家们把精力集中在保持大气清洁和免受污染上。

youdao