A. /, one
B. /, pair
C. a, pair
D. a, one

　　Nowadays you can buy a different kind of shoes specially designed for your
sport. If you are running on grass,it will be a good idea to have the right shoes for
the job-a pair of shoes which has studs(鞋钉) so that you don't slip(滑倒).
　　You do need to wear a mouth guard(保护器) for all ball sports where you
and the ball or another person could touch your face, You can buy a mouth guard
in a sports store,or your dentist will make one for you to exactly fit(适合) your
mouth. This will cost more but will be a good fit.
　　If you are traveling on skates you will need a well-fitting helmet to protect
the most important part of you    your head.
　　Knee and elbow guards are helpful too.
　　All of these gears(用具) cost money,but it will help to protect you from
harm. You may be able to get second-hand gear from older members of your
sport. It isn't safe for you to be playing sports or riding your skateboard or bike
without wearing the right gear to protect yourself.

1. What kind of shoes should you wear when running on grass?
                                                          
2. Which mouth guard is cheaper,the one bought in a store or the one made by a
dentist?
                                                          
3. How many kinds of gear does the writer mention?
                                                          
4. What should we do when we do sports according to the writer?