不管何种形式的点火能量必须达到一定()的才能引起燃烧反应。（A）浓度 （B）密度
题型：单项选择题
问题：
不管何种形式的点火能量必须达到一定()的才能引起燃烧反应。
（A）浓度
（B）密度
（C）强度
（D）速度
题型：单项选择题
There are about 80.000.000 mines under the ground in more than 60 countries. It is difficult and dangerous to clear these mines.About 50 people including many children were killed or hurt each day.In 2003，APOPO，a Duch research company that trains the animals,came up with the idea of using rats to search for the mines.
The animal trainers found that a kind of rats from Africa were clever and had a sharp sense of smell.The rats were about 75 cm long and weighted about 1.35 kg.light enough to run across a minefield without setting off the mines.
In January 2004，the APOPO startec this preject.First ,the trainers let the 4-week-old baby rats get familier with humans. A few weeks later，the rats were no longer afraid of people and the things around them.Then they were trained to connect a click sound with food.After the rats had learned that ,the trainers then taught them to tell the different between the smell of mines and other smells.When the rats could do it，the click was sounded and they were given a bit of bananas.The method was called clicker training.“The training isn’t easy.”said the trainer Adulish Mebomvu.“You have to be patient.Sometimes I get angry,but then again.I tell myself these are animals.”
After nine months’ training,the rats were taken to 4 minefield. They ran across the minefield ,stopped, sat and searched the ground to tell the deminers that they smelt out a mine. Then the mine was cleared.It had taken two deminers a day to clear a 200 m2 minefield. But with the help of two rats they could finish it in two hours.
The rats and the deminers saved thousands of lives.“The rats did this job much better than we expected.So far they have helpde to make almost 2.000.000 m2 of land safe.They are heroes.”said Bart Woetjcds.the head of the APOPO.
小题1:The APOPO trained the rats to search for__.
A．children
B．animals
C．minea
D．bananas小题2:While training the rats,the trainers have to be __.
A．patient
B．clever
C．brave
D．serious小题3:How long did the training last?
A．Two hours
B．One day
C．Four weeks
D．Nine month小题4:Which of the following is NOT TRUE acorrding to the passage?
A．Each day about 200 people were killed or hurt by minea
B．The APOPO started to train the rats is January 2004.
C．The trainers gave the rats food after they smelt out a mine .
D．The rats and the deminres saved thousands of livers.