Both a person's heredity and his environment help to shape his character.

She was so obstinate that she wouldn't adjust her opini...

单项选择题She was so obstinate that she wouldn't adjust her opinions.

Differences in positions adopted by oxygen and hydrogen...

单项选择题Differences in positions adopted by oxygen and hydrogen atoms account for variations in the crystalline structure of different forms of ice.

Recent studies have identified four major global enviro...

单项选择题Recent studies have identified four major global environmental risks— acid rain, ozone depletion, deforestation and the greenhouse effect.