单选题 OFF THE CHANNEL ISLANDS, California—Large numbers of giant endangered blue whales have gathered offshore attracting dozens of marine biologists who want to know why. Scientists aboard six ships from the National Oceanic and Atmospheric Administration and other experts are working on a three-week project this summer to tag and track the whales electronically. Three blue whales were tagged and followed last week, but scientists have seen many more. " This is cetascean soup out here," said Fred Benko, owner of a private charter boat that shuttles scientists to and from their research area. The mammals, some up to 30 metres long, have congregated about 30 kilometres west of the Channel Islands, which are about 40 kilometres southwest of Santa Barbara and 120 kilometres northwest of Los Angeles. Scientists first noticed the increase in blue whales in local waters in 1991, and a 1993 study indicated about 2,000 blue whales along the California coast. Preliminary research suggests that the Channel Islands National Marine Sanctuary contains the most concentrated blue whale population in the world. The US Government has listed the animals as endangered since 1966, victims of the over zealous whaling industry in the first half of the century. Scientists believe there once were 400,000 blue whales roaming the world' s oceans, but now only about 12,000. The blue whales feed on krill, bright red crustaceans similar to shrimp. But since the Channel Islands are hardly the only place where krill thrive, researchers wonder what else might be drawing the whales to the area. To tag the whales, scientists use a crossbow to fire a dart into blubber on the creature' s back. A computer records the depth and length of every dive the whale takes. " It' s important for me that people know that they have a treasure out here," said sanctuary Manager Ed Cassano. " This is something everybody should be proud of. It' s the jewel in the crown. "

单选题 What is the main idea of this passage?

单选题 Marine biologists want to know______.

单选题 What does the last sentence, "It' s the jewel in the crown" mean?

单选题 Why are the researchers interested in the feed of blue whale?