they are different from your own.

       When the weather turns warm, everyone wants to be in or around the water. Hanging out at the pool or the beach on a hot day is a great way to beat the heat.

       Most people don't think much about water 1—but they should. For people between the ages of 5 and 24, drowning is the second  2 cause of accidental death.

       It doesn't have to be that way,  3.By knowing how to stay safe and following a few simple guidelines, most water related accidents can be  4.

       It's a good idea to swim only in places that are watched over by a lifeguard. 5  can predict changing ocean currents, sudden storms, or other  6  dangers. In the event that something does go wrong, lifeguards are trained in  7  techniques.

       Swimming in an  8 body of water(like a river, lake, or ocean) is different from swimming in a pool. You need more  9 to handle the currents and other changing conditions in the open water.

       If you do find yourself  10  in a current, don't panic and don't fight the current. Try to swim parallel(平行) to the shore until you are able to  11  the current, which is usually a narrow channel of water.  12  try to make your way back to shore as you do so. If you're  13  to swim away from the current, stay calm and 14 with the current. The current will usually  15 ， then you can swim to shore.

       16  a very good swimmer who tries to swim against a strong current will get worn out. If you're going to  17  in open water, better take lessons that provide you with tips on  18  unexpected dangers.

       Some areas with extremely strong currents are  19 limits when it comes to swimming. Do your research so you know 20  not to swim, and pay attention to any warning signs posted in the area.

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 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 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.