问题 选择题

以下命题是假命题的是(  )

A.命题“若x2+y2=0,则x,y全为0”的逆命题

B.命题“若m>0,则x2+x-m=0有实数根”的逆否命题

C.命题“全等三角形是相似三角形”的否命题

D.命题“若a+5是无理数,则a是无理数”

答案

对于A,“若x2+y2=0,则x,y全为0”的逆命题为“若x,y全为0则x2+y2=0”是真命题;

对于B,因为x2+x-m=0判别式为△=1+4m,当m>0时,△=1+4m>0,所以x2+x-m=0有实数根,

所以命题“若m>0,则x2+x-m=0有实数根”为真命题,其逆否命题为真命题;

对于C,命题“全等三角形是相似三角形”的否命题为“两个三角形不全等则它们不相似”是假命题;

对于“若a+5是无理数,则a是无理数”是真命题;

故选C.

单项选择题

Congress makes the laws in the United States. It has two pans, which are more or less equal in power. They are known as the House of Representatives and the Senate. The House of Representatives is larger than the Senate whose 100 members (two from each state) serve for six years. The 435 members of the House are elected every two years, and the number from each state is determined by the population of the state. For example, California, which has a large population, has 43 representatives, while the State of Nevada has only one.

The House and Senate are divided into small groups which take care of special matters such as education or foreign affairs. The most important work of Congress is often done in these groups, which are called subcommittees.

According to the Constitution of the United States, a senator must be at least 30 years old and he must have been a citizen of the United States for nine years at the time of his election. To be elected to the House a person must be 25 years old and must have been a United States citizen for seven years. At the present time, members of Congress include businessmen, farmers, teachers, and especially lawyers. In general, senators are better known than representatives because they are fewer in number and serve for a longer time. Many American presidents served in Congress before they became president.

Which of the following is true().

A. A representative serves for two years.

B. To become a senator is easier than to become a representative.

C. A senator performs his duties for a shorter time than a representative.

D. All presidents were representatives and then senators before becoming president of the United States.

单项选择题