单项选择题

Questions 29 to 32 are based on the passage you have just heard.

A．Four years.
B．Five years.
C．Three years.
D．Six years.

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填空题

Scientists have developed a new cancer drug. So far, they have tested it only on (36) animals. The drug is designed to (37) and kill cancer cells but not healthy cells. First, the drug enters the cancer and destroys the supply of blood. Then it releases (38) to destroy the cancer cells. Researchers at the Massachusetts Institute of Technology in Cambridge carried out the study. The (39) appeared in Nature (40) . A school news release called the drug an anti-cancer smart bomb . Ram Sasisekharan is a professor at M.I.T. He says his team had to (41) three problems. They had to find a way to destroy the blood vessels, then to (42) the growth of new ones. But they also needed the blood vessels to supply chemicals to destroy the cancer. So, the researchers designed a two-part nanocell . The cell is (43) in nanometers, or one thousand millionth of a meter. (44) . The scientists say it was small enough to pass through the blood vessels of the cancer, but it was too big to enter normal blood vessels. The surface of the nanocells also helped them to avoid natural defenses. (45) . That cut off the blood supply and trapped the nanocell inside the cancer. Then, the nanocell slowly released chemotherapy drugs to kill the cancer cells. (46) .

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