如图所示，在x轴上方存在磁感应强度为B的匀强磁场，一个电子（质量为m，电荷量为q

某股份有限公司于20×0年3月30日，以每股12元的价格购入某上市公司股票50万股，作为短期投资;购买该股票支付手续贯等10万元。5月25日，收到该上市公司按每股0.5元发放的现金股利。12月31日该股票的市价为每股11元。20×0年12月31日该股票投资的账面价值为()万元。

A.550

B.575

C.585

D.610

下列运算正确的是   [ ]

A ．a²·a³=a⁵      

B ．(a²)³=a⁵        

C ．a⁶÷a²=a³        

D ．a⁵＋a⁵=2a¹⁰

蒸腾失水对果实贮藏的影响？

阅读理解。

     A British ship that sank during the American Revolution has been discovered at the bottom of

Lake Ontario.Surprisingly,the 22gun ship is wellpreserved in the cold,deep water.Explorers

announced the news recently.

     Kennard is an electrical engineer.He has been diving for nearly 40 years and has found more

than 200 wrecks(残骸) in the Great Lakes and other lakes or rivers.He began searching the

Ontario 35 years ago but quit after several dives.Six years ago,he began to work with Scoville,a

diver.Since then,the pair have found seven ships in the lake.Over the years,Kennard got licenses

and information,including the ship's design plans,from the British government.Even then,it took the

pair three years to search more than 200 square miles before they found the ship earlier this month.

     After locating the wreck with the sonal(声纳),the explorers used a submarine to confirm their

find.The 80foot ship is the only entire British ship ever found in the Great Lakes,Scoville and

Kennard said."To have a ship from the Revolutionary War that's nearly entire is unbelievable.It's

an archaeological miracle."They said the ship is still considered the property of the British Admiralty.

Although the ship sits in an area where the water is up to 500 feet deep and cannot be reached by

anyone but the most experienced divers,Kennard and Scoville refused to give its exact location with

care.They only said that it was found off the southern shore.

     The ship was discovered resting partially on its side.It went down on October 31,1780,with 60

British soldiers, a crew of about 40,mostly Canadians,and possibly about 30 American war prisoners.

The explorers also found two cannons and the ship's bell.

1．From the passage we learn that Kennard________.

A．has found over 200 wrecks in the Great Lakes

B．has kept searching the Ontario for 35 years

C．is both an engineer and an experienced diver

D．got to know Scoville when he was very young

2．Kennard and Scoville's discovery of the British ship ______.

A．cost them a lot of time and labor

B．needed a lot of experts's support

C．was forbidden by the government

D．was made completely by accident

3．We can infer from the text that Kennard and Scoville______.

A．will earn a great deal of money by selling the ship

B．will become world famous because of their find

C．may not have succeeded without modern technology

D．will be given a large reward by the American government

4．Kennard and Scoville refused to give the ship's exact location because________.

A．they did not know exactly where the ship was

B．they were afraid that something unexpected might happen

C．they wanted to keep it a secret forever

D．they thought it would be interesting for people to guess where it is

生活饮用水水质标准（GB5749—1985）中要求锌的含量范围是（）。

A、不大于1.5mg/L

B、小于1.0mg/L

C、不大于5.0mg/L

D、小于1.5mg/L