阅读理解
What do you do if you get hit in the mouth and one of your teeth is knocked out? A dentist may be
able to put the tooth back in for you, but you have to get to the dentist first. In the meantime, you have
to store the tooth so that it will stay healthy.
The simplest thing to do is to put the tooth back into your mouth, or you could put it in milk. Frank
Courts, a dentist at the University of Florida, worked with other researchers to find the safest way of
keeping knocked-out teeth. He tried putting teeth into milk, into water,  and into  cell-culture  medium
(细胞培养液).  He also tried just drying the teeth in the open air. He used teeth that had to be removed
from people's mouths for vanous reasons. The teeth were put into one of the solutions(溶液) or stored
in the air for one hour. Then cells from the root of the teeth were scraped off the teeth. Dr Courts and the
others then studied how healthy these cells were.
The cell-culture medium worked best to keep a knocked-out tooth healthy outside the mouth.
However, few people keep cell-culture medium handy at home or in school. The next best thing was
milk. But Dr Courts said that the best thing of all was to wash the tooth and put it right back into its
socket (牙槽) in the mouth. For some people, though, this is just too painful or upsetting.  So milk will
do, until you get your tooth( andyour mouth) to a dentist.

1. This passage is mainly about          .

A. how a dentist can save a knocked-out tooth
B. how to keep a knocked-out tooth healthy
C. how Dr Courts and other researchers made their experiments
D. how to put a knocked-out tooth back into its socket

2. Dr Courts tested __     .

A. man-made teeth
B. teeth dried in the open air
C. teeth pulled for various reasons
D. teeth put back in their sockets

3.The best way to keep a knocked-out tooth healthy outside the mouth is to store it       .

A. in cell-culture medium
B. in milk
C. in water
D. in the open air

4. Milk can be used instead of cell-culture medium to put a knocked-out tooth in because       .

A. milk works better to keep the tooth healthy
B. nulk causes less pain
C. cell-culture medium is not usually handy
D. cell-culture medium is more expensive

查看答案