10．Does stress cause gray hair？Many people believe that tension and stress can cause your hair to lose its color．In fact，it is an old wives tale that being upset all the time can result in premature（过早的） graying．Here is a closer look at this situation and why some believe that this old wives tale could be true．
As one ages，the hairs on the head also age．In fact，just about everything on the human body begins to show signs of wear and tear after a while．The joints wear and become stiff and skin wears and becomes wrinkled．Hairs on the head grow and eventually die．They are replaced，but in the process something else happens．
When new hairs are replaced，the color or pigment（色素）is also added to them．However，as one ages，this pigment becomes less and less available．At first，hairs will have a limited amount of pigment and they will appear to be grayish in color．In time，they will lose all of their pigment and will be white．Many things are known to cause graying．and genetics（遗传学） is a very powerful factor．If one of your parents turns gray at an early age，there is a good chance that you will too．Some people begin the graying process in high school，while others may be over the age of forty．
Constant worry and tension can have many harmful effects on the human body．It is a known fact that stressful times can cause one to suffer hair loss．It would make sense that if it can cause these problems，perhaps it also may contribute to graying．However，there is no sound evidence to support this．
On the other hand，many medical professionals believe that there may be a link：between graying and a constant state of anxiety or tension．Does stress cause gray hair？There is no scientific evidence to support the theory，but it is best to avoid stressful situations．
25．The underlined phrase in the first paragraph most probably meansA．
A．silly remarks
B．clever remarks
C．exciting remarks
D．disappointed remarks
26．The second paragraph mainly tells usB．
A．every part of body is replaced with age
B．every part of body ages with age
C．skin becomes wrinkled with age
D．hairs will grow weak but not die
27．From the passage we can infer thatC．
A．stressful situations can be of benefit．
B．gray hair has nothing to do with tension．
C．stress causing gray hair is still in question
D．sound evidence has been found．
28．What might play the most important role in the graying process？B
A．Genetics and the amount of sleeping time
B．The amount of pigment and genetics
C．The amount of food people eat and living environment
D．Genetics and the amount of water people drink．
