在存在的几百种神经递质中，已知的有几十种。

Dozens of neurotransmitters are known; hundreds may exist.

有几百种细菌都把人类的肠道看成自己的家园。

Hundreds of species of bacteria call the human gut their home.

他试着用棉花和几百种其他材料做成细碳条。

He tried cotton and hundreds of other materials to make this thin piece of carbon.

人们尝试过几百种治疗普通感冒的方法，但大多不成功。

People have tried hundreds of ways to cure the common cold, mostly without success.

去年国际上亮相了几百种疫苗，有效的只有三四十种，进入临床三期的只有两种，而且效果还不好。

Last year, several hundred international debut vaccination, the only effective San Sishi species into the clinic, there are only two of the three, but the effect is not good.