记得中学时，班里曾有男同学手里拿着粉笔假装吸烟，还真蒙了不少人。仔细想想，粉笔和香烟还真是张得很像，只不过前者是消耗自己为人类服务，而后者是燃烧自己来危害人类。像这样外形相似，实质却大相径庭的例子无处不在，比如我们今天要说的chalk and cheese。

Cheese is soft and white; chalk is hard and also white. The words chalk and cheese are similar, as they begin with the same sound. Although chalk and cheese have such similarities, they are very different from each other in taste and texture, and this is the point made by this expression.

奶酪和粉笔都是白色的，但奶酪质软而粉笔质硬。它们的另一个相似点是两个单词chalk和cheese的开头音节都是ch，开头发音相同。虽然chalk（粉笔）和cheese（奶酪）有上述相似之处，但是它们的构成和味道却是完全不同的，这也是chalk and cheese这个短语意思的由来。

For example:

Although they are brothers, they are as different as chalk and cheese.

虽然他们是兄弟，但是两人一点也不一样。www.51education.net