John's notebook entry: Mar 15, 2011 It's cold outside, and I got a terrible cold. It's spring now, and days getting warmer and warmer. But in this period of time, flu is easily broke out. The reason is that everyone took off their winter clothes, and put on their summer clothes; but the weather is not stable, a wave of cold air may lead to the sharp down of the temperature, so everyone get cold. As a saying goes, one should keep warn in spring and bear the cold in autumn. Our ancients find this rule from experiences. In spring ,we know the temperature will get higher, so we take off our heavy clothes, but cold air alwasy follows. While in autumn, it's become colder, and we feel that winter in coming. Many of us put on our winter clothes. But it's no really winter ,it's just autumn. We put on our clothes too early to bear the freezing temperature in cold winter.