题目内容：

    Giant, krill-eating whales could grow even bigger if the size and availability of their prey (猎物）could keep up，a new study finds.

Whales are the heaviest animals to have ever lived on our planet. These marine giants evolved from dog-sized four-legged land creatures and grew nearly 10,000 times bigger in the past 50 million years or so, according to Nicholas Pyenson, head of fossil marine mammals at the Smithsonian's National Museum of Natural History.

Creatures benefit from having a bigger size in a number of different ways, whether it’s not getting eaten by smaller creatures or having the ability to keep warm and travel great distances more efficiently. Still, some whale species are bigger than others, and they do have some limits to their size.

To find out what these limits are， researcher attached multisensor equipment to many types of whales. The researcher also assessed prey type and quantity using different methods. For baleen whale prey，they used acoustic(声学的) equipment to test the density (密度）of krill patches. For toothed whales, they looked at the size and quantity of squid(鱿鱼）beaks and otoliths (parts of the inner ear) found in the stomachs of beached whales.

Putting all the data together, they could determine how much energy the whales were likely to get back from the food. For toothed whales, the limiting factor seems to be the size of their prey. Sperm whales were found to feed mostly on medium-sized squid—possibly because there aren’t as many giant squid in the ocean. Baleen whales, like blue whales swallow massive mouthfuls of krill or other small creature. But these small creatures only appear in large concentrations for a few months per year in some areas ,which may be the limiting factor for the growth of the largest whales.

A researcher said that it ‘s not completely clear that baleen whales have finished growing. “Perhaps several million years into the future we’ ll see something even larger than a blue whale.”

1.What can we infer from the second paragraph?

A.Whales kept growing during evolution.

B.Whales evolved from dogs on the land.

C.Whales used to be four-legged fish.

D.The number of krill-eating whales would keep up.

2.How do whales benefit from their size?

A.They are more expert at traveling.

B.They can produce energy more easily.

C.They have better chances to survive.

D.They can be eaten by smaller creatures.

3.How did the researchers carry out the study?

A.Testing the density of whales with acoustic equipment.

B.Using different methods for different types of whales.

C.Calculating the amount of food in baleen whales’ stomachs.

D.Assessing the type and quantity of different whales.

4.What may stop whales from growing even bigger?

A.The amount of food.

B.The availability of equipment.

C.The size of their stomachs.

D.The concentrations of the whales.