nitrogen

我们呼吸的空气中约78%是氮气。

About 78% of the air we breathe is ___nitrogen.

科学家们用液氮来保存重要的生物样本。

Scientists use liquid ___nitrogen to preserve important biological samples.

这种新型肥料含有丰富的氮元素，能有效促进植物生长。

This new fertilizer contains high levels of ___nitrogen, which helps plants grow better.