human being是可数名词可以加a和复数human beings
1 How long can a human being go (ie survive) without food?
2Although the Negroes were humanbeings just like the whites they were not treated as humanbeings.
后面指的是生物体 也是可数的
1 Are you quite sure there is no living beings on Mars?
2 (linguistics) belonging to the class of nouns that denote livingbeings.
如果不确定可以查阅朗文词典online /
和剑桥词典 http://dictionary.cambridge.org/