They were deglycerolized by alternately centrifuging and mixing; he planted fir and pine trees alternately.是什么意思？

They were deglycerolized by alternately centrifuging and mixing; he planted fir and pine trees alternately.

交替运用离心法和混合法来除去他们的甘油渍; 他交叉种植冷杉和松树.

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

by

prep. 在…旁边，表示方式，由于，经过；adv. 经过，表示保留或保存时用，短暂拜访；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

alternately

adv. 轮流地，交替地，交互，更番；

例句
He could alternately bully and charm people.
他一会儿欺负人一会儿取悦人。

centrifuging

n. 离心法，离心过滤；

例句
They were deglycerolized by alternately centrifuging and mixing.
通过交替性离心过滤和混合,它们被去掉甘油.

and

conj. 和，与，而且，于是，然后，因此；

例句
I spend a lot on expensive jewelry and clothing...
我花很多钱购买昂贵的首饰和衣服。

mixing

n. 混合，混频；v. 混合( mix的现在分词 )，（使）结交，相容，平安相处；

例句
Pour the melted butter into a large mixing bowl.
把熔化的黄油倒在一个搅拌用的大碗里。

he

pron. 他，它，一个人；n. 雄性动物；

例句
Logic had prevailed and he had abandoned the idea.
最终理智占了上风，他打消了那个念头。

planted

v. 种植( plant的过去式和过去分词 )，建立，移植（动物、植物），在（某处）栽种；

例句
It's not known who planted the bomb...
安放炸弹者身份不明。

fir

n. 冷杉，[植]枞木；abbr. food-irradiation reactor 食物辐射（杀菌）用反应堆，firkin 弗京；

例句
...a bowl of fir cones.
一碗冷杉树球果

pine

n. 松树，松木；vi. 憔悴，痛苦，渴望；vt. 为…悲哀，哀悼，消瘦，渴望，渴慕；

例句
A thrush alighted on a branch of the pine tree.
一只鸫落在松树的树枝上。

trees

n. 树（ tree的名词复数 ），乔木，树状图，世系图；

例句
...Christmas trees decorated with coloured baubles.
缀满各色小饰物的圣诞树