Many people believe that yellowing and wetness are the greatest enemy of stamps. In fact, stamps are afraid of not only wetness, but also light and dirty things. People protect their stamps in several different ways.
To protect stamps,we should never touch the stamps with our hands.This avoids moving dirty things onto them. Stamp tweezers (镊子) should be used in all conditions.
Stamps are printed things. The colour will slowly disappear if the stamps are put in the light for a long time. So we should not put stamps in the light for long. Direct sunlight must be avoided as well.
Wetness is an important problem for stamps. Some collectors will put stamps in separate plastic (塑料) bags. However, it is possible that some stamps have taken in some water from the air before they are put into the plastic bags.Stamps yellow easily and rapidly after they take in wet air.To protect the stamps, some people also put the stamps into a special room which has a machine to keep the air cool and dry. However, not many people can afford that.
To keep stamps, stamp collectors usually put them under plastic covers. It is a common and simple way. This helps because the plastic cover keeps the stamps off the wet air. It also stops the fingersfrom touching te stamps.
Some collectors prefer to store stamps inside a plastic box with desiccants (干燥剂).However, we should take care not to let the stamps. touch the desiccants. On top of that, don't take your stamps out on a wet day.
,若
,则
的值等于（ ）
