The last sentence in the last paragraph implies that ______.
A.it is difficult to cool the engine
B.the driver can only open the hood on a hot summer day
C.the driver has to be very patient
D.it takes a long time to open the hood in summer
The last sentence of the text shows that
A.Van Oss has full confidence in the developers and the public in using new concrete.
B.Van Oss is pessimistic about the future development of greener concrete.
C.Van Oss is hostile to the attitudes of developers and the public.
D.Van Oss feels that people should be patient to wait for the change of the public attitude.
That may be about to change. This week, America's Food and Drug Administration gave its approval to a new type of artificial heart made by Abiomed, a firm based near Boston. The agency granted a "humanitarian device exemption", a restricted form. of approval that will allow doctors to implant the new device in people whose hearts are about to fail but who cannot, for reasons such as intolerance of the immunosuppressive drugs needed to stop rejection, receive a transplant. Such people have a life expectancy of less than a month, but a dozen similarly hopeless patients implanted with Abiomed's heart survived for about five months.
Unlike Dr. Jarvik's device, this newfangled bundle of titanium and polyurethane aims to set the patient free. An electric motor revolving up to 10,000 times a minute pushes an incompressible fluid around the Abiomed heart, and that fluid, in turn, pushes the blood—first to the lungs to be oxygenated, and then around the body. Power is supplied by an electric current generated in a pack outside the body. This induces current in the motor inside the heart. All diagnostics are done remotely, using radio signals. There are no tubes or wires coming out of the patient.
The charger is usually plugged into the mains, but if armed with a battery it can be carried around for hours in a vest or backpack, thus allowing the patient to roam freely. Most strikingly, the device's internal battery can last half an hour before it needs recharging. That allows someone time to take a shower or even go for a quick swim without having to wear the charger.
Abiomed's chairman, Michael Minogue, does not claim that his firm's product will displace human transplants. Even so, the firm has big ambitions. It is already developing a new version that will be 30% smaller (meaning more women can use it) and will last for five years. That should be ready by 2008— 320 years earlier than the writers of "Star Trek" predicted.
"Star Trek" is mentioned in the text so as to______.
A.depict the long history of artificial hearts in science fiction
B.enumerate artificial hearts of all sorts on sale
C.provide background for the discussion of artificial hearts
D.emphasize the great efforts made by Yamaha and Jensen in the development of artificial hearts
题图中,已知机构各部分尺寸:lAC=lBC=lCD=lCE=lDF=lEF=lFG=lFH=lGI=lHI=10mm,设两滑块以等速v1=v2=0.002m/s,沿相反方向滑动,求图示位置(φ3=45°)时速度比值vI/v1。