一般而言，对危险性较大的系统可采用系统定性、定量的安全评价法，工作量也大。（）

     Bill is only fifteen years old, but he's already very rich. Two years ago, Bill began football website
(网站) for young people. "I became interested in computers when l was eight because my father's job
is with computers. As a little boy, I also loved football.   1  ".
     Bill started the "Football OK!" website two years ago, and now more than 20,000 people visit it
every day.
       2   He usually gets up at six and looks at his emails. Then he goes to school from nine to four. In the
evenings, he always works for about four hours on his website.
       3  "At the moment I am thinking about a new website on American football, maybe for next year," 
he said.
     And is Bill the same person that — he was three years ago?    4   "I have met a lot of interesting
people on the website and I have traveled all over the world." Bill doesn't know about the future. "Maybe 
I will sell the website. I really don't know. I'll just wait and see."
     When he is 21, Bill will be a millionaire (百万富翁). He always says, "Anything is possible."