“二次派送”有何规定？

两个做匀速圆周运动的物体，其质量之比为m₁：m₂=2：3，角速度之比为ω₁：ω₂=3：2，线速度之比为v₁：v₂=6：5，则它们的轨道半径之比为r₁：r₂=           ，向心加速度之比为a₁：a₂=           ，向心力之比为F₁：F₂=          。

下列哪种症状不是精神分裂症的特征性症状：（）

A.思维破裂

B.评论性幻听

C.思维中断

D.思维插入

E.思维不连贯

B

What weighs 3500 pounds(1600kg)and lived 60 million years ago?Are you thinking of

dinosaurs?Guess again!You don,t have to go to a museum to see these creatures．They are alive

and swimming in the warm coastal waters of Florida．

Manatees(海牛)have lived a peaceful existence in the warm waters  of  Florida  for  60

million years．However，they are now an endangered species．This means that if humans don,t do

something to save them，they will soon go the way of dinosaurs．

Humans have made life very difficult for manatees．One big danger that humans have

introduced is the speedboat．Because manatees are mammals．they need to come to the surface to breathe about every 5 to 6 minutes．This means that they are in constant danger of being caught in the propellers(螺旋桨)of speedboats．And boating aceidents are the greatest cause of death for them．

Manatees are in extra danger when they are in their sleeping or“torpor”state．They still

have to come to the surface for the air，but sometimes they are too sleepy to avoid the danger of approaching boats．

Another danger for manatees is the pollution that humans produce．Due to human pollution，

a deadly plant called red tide had increased greatly in the Gulf of Mexico．The plant，or algae，

t11riVes(繁茂)on pollution．It wiped out nearly 20 percent of the total manatee population on

earth．

Humans can help to save manatees。The government has established boating speed limits to

give the manatees．a chance to escape approaching speedlsoats．Everyone can help by cutting

down on waste and pollution to protect the waters for the manatees．

One famous singer，Jimmy Buffet，has helped save the manatees．He co-founded the Save the Manatee Club(SMC)．SMC had begun an adoption(收养)program for the manatees．For a fee，sponsors(资助者)can name a manatee．Donations are used to help protect the manatees and their habitat．

45．The manatee is the kind of animal that___________．

A．1ikes living in the cold waters of Florida      B．will die out if not protected in time

C．call dive in the deep sea for hours             D．is the biggest living animal on earth

46．Why is it dangerous for manatees to be in a torpor state?

A．Because they come to the snlface to breathe，and that is when they are hunted．

B．Because they eat deadly algae，and this makes them too sick to avoid danger．

C．Because they live in groups and therefore they are easily hurt by passing boats．

D．Because they are sleepy when they surface，so they can,t avoid approaching boats．

47．The death of the manatees is largely due to__________．

A．human hunting                       B．human pollution

C．speedboat accidents                  D．deadly plants

48．To help protect manatees，people should_________．

A．never go speed boating in their living habitat

B．keep the waters of Florida free from pollution

C．have manatess named by sponsors without a fee

D．wake manatees up from their torpor state

A vessel moored with two anchors,sometimes, at an exposed roadstead to（）.

A.aid turing the ship

B.obtain a fine bearing

C.increase ship swing to wind or tide

D.lighten the stress of anchor chains

数据库的三级组织结构中，用户视图是 【14】 。