Chemists had been studying the atmosphere for about two thousand years before its composition was discovered.

化学家们一直在研究大气，研究了约两千年，它的组成才被发现。

youdao

Chemists had been studying the atmosphere for about two thousand years before its composition was discovered.

化学家们一直在研究大气，研究了约两千年，它的组成才被发现。

youdao