Recently, a scientist did some experiments．He left a group of 4-year-olds in a room with a bell and a candy．If they rang the bell, he would come back and they could eat the candy．If, however, they didn't ring the bell and waited for him to come back on his own, they could then have two candies.
In videos of the experiment, he can see the children kicking, hiding their eyes--trying to exercise self-control so they can wait and get two candies．The results are different．Some broke down and rang the bell within a minute．Others lasted 15 minutes.
The children who waited longer went on to get higher SAT scores．They got into better colleges and had better adult success．The children who rang the bell quickest were more likely to have received worse teacher and parental evaluations （评价） 10 years later and were more likely to have drug problems at age 32.
The experiments are worth noting because people spend a lot of time thinking about how to improve education, how to become rich．But when the result is not good, they will come back to ask "how do we get people to get the sort of self-control that leads to success?" This is to enter the world of human nature.
So these experiments along with everyday experience, tell us that self-control is most important．Young people who can sit through sometimes boring classes to get a degree can work hard in order to learn a language well．They can avoid drugs and alcohol．For people without self-control skills, however, school is a series of failed ordeals（煎熬）．No wonder they drop out and their later life is a group of foolish ideas, such as drug use, stealing and so on.
The scientist did some experiments to         .

A．test children's self control and later success

B．test children's intelligence of ringing the bell

C．find good ways of training children to learn

D．prove that children's education is important

We can learn from the experiment that        

A．all children tried to ring the bell for more candies

B．some children didn't get any candy in the end

C．the children have different self- control

D．the last one to ring the bell is most successful

What is the best title for this passage?

A．Ways of self-control training

B．Experiments on children's ringing the bell

C．Higher score, better achievements

D．Self-control is the key to success