下列说法正确的是（ ） A．减少热机的工作时间，可以提高热机的效率 B．一杯煤

按旅游活动开展的地理范围分，旅游可分为()。

A.国际旅游

B.专业旅游

C.国内旅游

D.观光旅游

金刚石、石墨、木炭和C₆₀都是由碳元素组成的单质，下列关于碳的单质的叙述正确的是（　　）

A．都是黑色固体

B．在氧气中充分燃烧时都生成二氧化碳

C．碳原子的排列方式相同

D．一定条件下，石墨转化成金刚石是物理变化

Most taxpayers have had enough income tax collected by their employers during the year. So they do not (36) any money. In fact, most Americans get some money back. Last year, the Internal Revenue Service returned at least some money to more than (37) Americans paying individual income tax.
The United States has what is called (38) . Tax rates increase as (39) increase. This year, people earning more than (40) are taxed at the highest rate.
Earnings above that amount are taxed at (41) . Earnings below that amount are taxed at lower rates.
Individuals who earn less than (42) pay no income tax. But they do pay (43) , Medicare and other taxes.
There are many different ways for people and businesses to reduce their (44) Most homeowners, for example, can reduce their taxes a little by reporting to the I.R.S. the interest they pay (45) . This is called a (46)
In 2004, personal income taxes provided the government with most of its money: (47) of the budget. Social security and other (48) taxes provided (49) . Other forms of income include (50) , money borrowed to (51) and special taxes on (52) .
But income from taxes did not provide enough to pay for government spending. The I.R.S. says the budget deficit for 2004 was about (53) dollars.
Preparing tax documents can be complex. The I.R.S. estimates that taxpayers need an average of about 13 hours to prepare tax documents. And that is just for the basic tax form. For business, the I.R.S. estimates an (54) needs more than 50 hours. This is why a lot of Americans pay (55) to complete their tax documents for them.

急性心力衰竭伴快速房颤的病人首先应当考虑哪种治疗（）

A.控制呼吸道感染

B.控制心室率

C.纠正电解质紊乱

D.控制液体入量

E.加强利尿

鱼类急性毒性测定时，换水式试验需（）h更新一次试验液。

A.2～8

B.8～24

C.24～48