实验室检测立克次体时，最常用的人体标本是（）

A.尿

B.粪便

C.血液

D.头发

E.痰

People have cooked over open fires and dirty stoves for all of human history, but the simple fact is they are slowly killing millions of people and polluting the environment. Engineers and development professionals have worked on this problem for decades. My own involvement stretches back many years, and I’m well aware that well-meaning efforts have been launched, but none have managed to match the scope of the challenge.