题目内容：
Explorer of the Extreme Deep Oceans cover more than two—thirds of our．planet．Yet，just，a small fraction of the underwater world has been explored．Now，Scientists at．the Woods Holel Oceanographic institution(WHOI)in Massachusetts are building an underwater vehicle that will,carry explorers as deep as 6，500 meters(21，320 feet)．The new machine，known as a manned submersible or human—operated vehicle(HOV)，willrep]ace another one named Alvin2 which has an amazing record of discovm7，playing a key．role in various important and famous undersea expeditions．Alvin has been operating for 40 years but can go down only 4，500 meters(14，784 feet)．It’s about time for an w/grade，WHOI researchers say． Alvin WaS launched in：1964．Since then，Alvin has worked between 200 and 250 days a year，says Daniel Fornarl．a marine geologist al3d director of the Deep Ocean Exploration Institute at WHO—During its lifetime，Alvin has
cmried some l2，000 people on a total of more than 3，000 dives。
A newer，better；versions of Alvin is bound to reveal even more surprises aboul，a world that is still full of mysteries，Fornari says．It might also make the job of exploration a little easier，“We take so much for granted on land，”Fornari says．“We can walk around and see with our eyes how big things are．We can see Colors，special arrangements．”
Size—wise，the new HOV will be similar to Alvin。It’ll be about 37 feel，long．The setting area inside will be a small sphere，about 8 feet wide，like Alvin，it’ll carry a pilot and two passengers．It will be just as maneuverable．In most other ways，it will give passengers more opportunities to enjoy the view，for one thin9。Alvin has only three windows，the new vehicle will have five，with more overlap so that the passengers and the pilot．can see the sarab thing．
Alvin can go up and down at a rate of 30 meters every second，and its maximum speed is 2 knots(about 2.3 miles per hour)，while the new vehicle will be able to ascend and descend at 44 meters per second．It’ll reach speeds of 3 knots，or 3.5 miles per hour．词汇：
manned adj．载人的 sphere n．球体；范围
undersea adj．海底的 maneuverable adj．机动的，可调动的
submersible n．潜艇；潜水器 overlap v．n．重叠根据以上材料回答下面问题：What is Alvin? A．A research institut
B．A transporting vehicl
C．A submersibl
D．A scientis
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