Like the rest of their species，the Southern Hemisphere humpback whales typically prefer to remain single or gather in small groups that disperse （散開） quickly．However，since 2011，researchers from Cape Peninsula University of Technology in Cape Town have been observing a new phenomenon off the coast of South Africa．Professor Ken Findlay and his team reported seeing 22 cases of large groups of humpback whales on three different occasions in 2011，2014，and 2015．
The researchers are puzzled not just by the unusual social behavior，but also by the fact that the"super-groups"were seen in April and May．That's because the mammals typically spend these late summer months （in the Southern Hemisphere） feeding in the Antarctic waters before heading back to the warmer subtropical South African waters during winter，to breed and give birth．In a study published in the journal PLOS ONE on May 1，F(xiàn)indlay and his team outlined some of the possible reasons behind the big change in the mammals' behavior．
The researchers say that the cause of the recent sightings could be the abundant food available in the Benguela upwelling system．Located near the southwestern tip of South Africa between St．Helena Bay and Cape Point，the system of cold，nutrient-rich ocean currents is rich in phytoplanktons and species of small fish that the humpback whales feed on，such as the mantis shrimp．
Another probable reason is the sudden increase in humpback whales' population．According to a recent scientific report，the mammals，population，off the coast of Australia，has reached nearly 90 percent of pre-whaling numbers，while on the US East Coast，the number of whales is up 60 percent from its lows．All in all，experts estimate there are currently 150，000 humpback whales swimming in our oceans．They all need to feed．
However，while the theories may explain the decision to skip migrating （遷徙） to Antarctic waters，the reason for the social super-groups remains a mystery．According to Findley，"It's possible that the behavior was occurring，but just not where it was visible （看得見的）．Because there were so few of them，we may not have seen it．"

（1）What is implied about the humpback whales in Paragraph 2？

C

C

A．They no longer hunt for food in the Antarctic waters．
B．They usually spend the whole winter in the Antarctic waters．
C．They are rarely seen in South African waters during April and May．
D．They've changed their social behavior to adjust to the warmer waters．
（2）According to Findley，why are the humpback whales seen in large groups now？

B

B

A．Because they swim in populated areas now．
B．Because their number has increased greatly．
C．Because they need to work together to hunt for food．
D．Because researchers pay closer attention to them now．
（3）What does the passage mainly talk about？

C

C

A．Reasons for the number of humpback whales increasing so greatly．
B．How humpback whales adapt themselves to the changing environment．
C．Why humpback whales appear off the coast of South Africa in large groups．
D．Researchers' findings about a new whale species near the coast of South Africa．