绒毛活检应在：（） A．孕6～9周  B．孕36周起  C．孕24～36周  D．孕

已知|a|=8，|b|=5，且|a+b|=a+b，求a﹣b的值  

已知A与a、B与b分别位于两对同源染色体上，现用基因型为AABB与aabb的个体进行杂交，产生的F₁再自交产生F₂，则下列说法正确的是[ ]

A．若两对等位基因分别控制两对相对性状，则F₂的双显性中杂合子占8/9

B．若两对等位基因分别控制两对相对性状，则F₂中纯合子占1/4

C．若两对等位基因控制同一对相对性状，且只要存在一个显性基因，个体便表现为显性，则F2的表现型比例为15：1

D．若只有A、B同时存在，个体才表现为显性，则F2的表现型比例为9：7

封闭式基金的募集合同期限为( )年以上。

A．1

B．2

C．3

D．5

Today about 70 countries use Daylight Saving Time (DST). Daylight Saving was first introduced during World War I in Australia. During the world wars, DST was used for the late summers beginning January 1917 and 1942, and the full summers beginning September 1942 and 1943.  

In 1967, Tasmania experienced a drought（干旱）. The State Government introduced one hour of daylight saving that summer as a way of saving power and water. Tasmanians liked the idea of daylight saving and the Tasmanian Government has declared daylight saving each summer since 1968. Persuaded by the Tasmanian Government, all states except two passed a law in 1971, for a test use of daylight saving. In 1972, New South Wales, South Australia and Victoria joined Tasmania for regular daylight saving, but Queensland did not do so until 1989.

Tasmania, Queensland and South Australia have had irregular plans, often changing their dates due to politics or festivals（节日）. For example, in 1992, Tasmania extended（延长）daylight saving by an extra month while South Australia began extending daylight saving by two weeks for the Adelaide Festival. Special daylight saving plans were made during the Sydney 2000 Olympic Games.

The differences in daylight saving in Australia continue to cause serious problems in transport and many other social activities. It also reduces the number of hours in the working day that are common to all centers in the country. In particular, time differences along the east coast cause major differences, especially for the broadcasters of national radio and television.

小题1:Daylight Saving Time was introduced in Tasmania _______________.

A．to stop the drought in 1967

B．to support government officials

C．to pass a special law in the state

D．to save water and electricity小题2: According to the text, which state was the last to use DST?

A．Victoria.

B．Queensland.

C．South Australia.

D．New South Wales.小题3: What can we learn about DST in some Australian states?

A．It doesn’t have fixed dates.

B．It is not used in festivals.

C．Its plan was changed in 2000.

D．It lasts for two weeks.小题4: What do we know about the use of DST from the last paragraph?

A．There exist some undesirable effects.

B．It helps little to save energy.

C．It brings about longer working days.

D．Radio and TV programs become different.

(A/P，i，n)表示( )系数。

A．资本回收系数

B．偿债基金系数

C．普通年金现值系数

D．普通年金终值系数