问题描述：
化学类的英语,有一句看不懂……帮帮忙……各位大侠
At the beginning of the 20th century there was a shortage of naturally occurring,nitrogen-rich fertilizers
这句啥意思哇……哭了……就知道前面是‘在20世纪初’……后面就不懂了……连不起来……帮忙下吧……
At the beginning of the 20th century there was a shortage of naturally occurring,nitrogen-rich fertilizers
这句啥意思哇……哭了……就知道前面是‘在20世纪初’……后面就不懂了……连不起来……帮忙下吧……
问题解答：
我来补答展开全文阅读