树是节点的集合，它的根节点数目是A．有且只有1 B．1或多于1 C．0或1 D．至少

通过实验得出空气是由氧气和氮气组成的科学家是 [ ]

A. 舍勒

B. 普利斯特里

C. 拉瓦锡

D. 道尔顿

下列实验能达到预期目的的是

[ ]

A.①

B.②

C.③

D.④

不属于社区健康教育与健康促进重点人群的是

A．儿童和青少年
B．妇女
C．青壮年
D．老年人
E．残疾人

Part 3

Questions 19-25

·Read the following passage and answer questions 19-25.
·For questions 19-25, choose the correct answer A, B, C and D.
·Mark your answers on the Answer Sheet.
While still in its early stages, welfare reform has already been judged a great success in many states, at least UN is getting people off welfare, lt’s estimated that more than two million have left the roles since 1994.
In the past four years, welfare in rolls in Athens country has been cut in half. But 70 percent of the people who left in the past two years took jobs that paid less than $6 an hour. The result: The Athens country poverty rate still remains at more than 30 percent—twice the national average.
For advocates for the poor, that’s an indication that much more needs to be done.
"More people are getting jobs, but it’s not making their lives any better," says Kathy Lairn, a policy analyst at the center in budget and policy priorities in Washington.
Canter analysis of US census data nationwide found that between 1995 and 1996, a great percentage of single, fame-headed household were earning money on their own, but that average income for these households actually went down.
But for many, the fact that poor people are able to support themselves almost as well without government aid as they did with it is in itself a huge victory.
"Welfare was a poison. It was a toxin that was poisoning the family," says Rector, a welfare reform is changing the moral climate in low-income communities. It’s beginning to rebuild the work ethic, which is much more important.
Mr. Rector and others argued that once "the habit of dependency is cracked," then the country can make other policy changes aimed at improving living standards.

Why aren’t people enjoying better lives when they have jobs

A．Because their wages are low.

B．Because many families are divorced.

C．Because the cost of living is rising.

D．Because government aid is now rar

用盘形铣刀在铣床上铁削做螺旋槽，工作台应（）转动一个螺旋角。