Hemoglobin, as you know, is an oxygen carrier and so red blood cells concentrate in bags of hemoglobin which circulate in your blood and they carry oxygen.

如你所知，血红蛋白是氧气的载体，所以红细胞集中在血红蛋白的袋子里，血红蛋白在血液中循环，它们携带氧气。

These groups concentrate in the inner cities.

这些人集中在内地城市。

Birds concentrate in places where food is abundant.

鸟聚集在食物丰盛的地方。

His third army was now directed to concentrate in Louisiana.

第三军团奉命集结于路易西安那州。

I no longer looked bright, and I couldn't concentrate in school.

我不再显得生气勃勃。我在学校里也无法集中注意力。