单项选择题
A．since the last century B．for a very long time C．since a few hundred years ago D．since a few years ago
A．people feel cool when they are near a lake or an ocean B．scientists can explain everything we want to know C．scientists can explain many things but not everything D．the salt in the ocean comes from rocks
A．To recognize worthwhile contributions to humanity. B．To resolve political differences. C．To honor the inventor of dynamite. D．To spend money.