Why does our hair become white as we get older? STEPHANIE NLSI Lui Kwok Pat Fong College Illness or stress may lessen the secretion of pigment, which normally gives colour to hair, and cause the hair shaft to whiten. However, the normal process of whitening that comes with age is determined by heredity. The colour of hair is determined by the amount of pigment and air spaces in the hair shaft. Hair colour and texture can be inherited. Why do students never get zero in the Scholastic Aptitude Test (SAT) in the United States? American educators adopted the 200 to 800 scale because they were concerned a zero mark would affect a student's self-esteem, something which doesn't seem to worry Hong Kong teachers. Likewise, an 800 doesn't mean you know everything - it's simply the top reported score. What students never see is their raw score. The highest raw score you can get in the verbal test is 85 because there are 85 questions. What happens to the umbilical cord inside a baby after he is born? As you may know, the cord is cut at birth and clamped. If the cord isn't clamped, the baby can lose a lot of blood and even die. But that's unlikely because there's an adrenaline- like hormone in the baby's body that causes the blood vessels inside the umbilical cord to collapse. These blood vessels are sealed off from the rest of the baby's circulatory system and eventually disappear altogether. So this leaves an external stump that dries up and falls off in a few weeks - leaving your belly button - and an internal stump that collapses and vanishes. Why do short naps seem to work so well? Naps are a matter of great interest to scientists. Sleep has no easily understood neurological benefit. We know that almost every creature sleeps and humans also have a natural inclination to nap. But experts say there is an epidemic of drowsiness- related accidents. As many as 40 per cent of car accidents are due to inattention, they say. 'Microsleeps', brief moments when your brain seems to nod off, can intrude into your wakefulness. So even a short nap of seven minutes or so can cure your sleepiness.