How is air pollution endangering your health and what can be done about it?
Air pollution, affecting over 99% of the global population, leads to a 20% increase in respiratory illnesses and other health ...
BBC10 小时
The human reproductive system
Most girls begin puberty between ages 8 and 14, with an average of 11. Girls develop more quickly than boys and most finish puberty within four years. Most boys begin puberty between ages 9 and 14 ...