This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.

I arranged to meet him at dusk.

The population density of this area is very high.

I am majoring in microbiology at university.

Astrobiology is a very interesting field of study.

I am majoring in microbiology at university.

He is an expert in paleontology.

He is an expert in aerobiology, engaged in the study of microorganisms in the atmosphere.

He is very interested in paleontology.

I am majoring in Biochemistry at university.