Health is something we tend to ignore when we have it. When our body is doing well, we are hardly aware of it. But illness can come even when we are young. In fact, childhood has been a very _____ (631) time. ______ (632), and people know very little how to cure them once they struck.______ (633). About a century ago, however, scientists found out about germs, and then everything changed. The reason of many diseases was found, and ______ (634) whichwere developed.

As this medical discovery spreads, the world became much safer for children. The result is that whereas hundred years ago, the average man lived for 35 years, nowadays, in many areas of the world, people can expect to live for 75 years. And what do we expect by the year 2020? Undoubtedly, medical science will continue _______ (635). Some people will be able to avoid medical problems that are unavoidable today.

But illness can come even when we are young. In fact, childhood has been a very _____ (631) time.