Raising a baby takes a lot of work, especially when that baby is a king penguin. Now, it looks like climate change will make life even harder for these birds. A new study suggests that warmer waters could make their numbers  _  Most king penguins live on the Crozet Archipelago, a group of islands in the Indian Ocean, about 1,000 miles north of Antarctica. After the penguin chicks are born in November (which is summer in the Southern Hemisphere), both parents spend 4 months collecting fish to feed their children. When the fish move to deeper waters in March, the adults leave their chicks alone for months. They swim hundreds of miles south. There, near the Antarctic ice, they spend the winter eating seafood, such as squid, to add their own energy stores. In October, nearly a year after their chicks are born, the parents return to feed and finish raising them. Scientists from the French National Center for Scientific Research (CNRS) in prefix = st1 /Strasbourg,France, have been studying king penguins on the Crozet Archipelago for a decade. Starting in 1998, Yvon Le Maho and other researchers implanted electronic ID tags under the skin of hundreds of penguins. The tags have allowed Le Maho's team to know the details about them, such as how long they live, whether they return from their winter trips, and if their chicks manage to survive the winter. Ocean surface temperatures vary from year to year. And former research had shown that fewer squid, fish and other creatures grow when the water is warmer. Le Maho suspected that this drop in the food supply would make it harder for adult penguins to survive the tough times ahead. King penguins can live for up to 30 years. And for now, the population still appears healthy. But a warming trend could cause big trouble for a bird that depends on cold and ice. According to the passage, the adult penguins spend the winter south because   _  .
They have to raise their children there they have to raise their chicks there the food supply they need exists there they have to give birth to chicks there
Question: Raising a baby takes a lot of work, especially when that baby is a king penguin. Now, it looks like climate change will make life even harder for these birds. A new study suggests that warmer waters could make their numbers  _  Most king penguins live on the Crozet Archipelago, a group of islands in the Indian Ocean, about 1,000 miles north of Antarctica. After the penguin chicks are born in November (which is summer in the Southern Hemisphere), both parents spend 4 months collecting fish to feed their children. When the fish move to deeper waters in March, the adults leave their chicks alone for months. They swim hundreds of miles south. There, near the Antarctic ice, they spend the winter eating seafood, such as squid, to add their own energy stores. In October, nearly a year after their chicks are born, the parents return to feed and finish raising them. Scientists from the French National Center for Scientific Research (CNRS) in prefix = st1 /Strasbourg,France, have been studying king penguins on the Crozet Archipelago for a decade. Starting in 1998, Yvon Le Maho and other researchers implanted electronic ID tags under the skin of hundreds of penguins. The tags have allowed Le Maho's team to know the details about them, such as how long they live, whether they return from their winter trips, and if their chicks manage to survive the winter. Ocean surface temperatures vary from year to year. And former research had shown that fewer squid, fish and other creatures grow when the water is warmer. Le Maho suspected that this drop in the food supply would make it harder for adult penguins to survive the tough times ahead. King penguins can live for up to 30 years. And for now, the population still appears healthy. But a warming trend could cause big trouble for a bird that depends on cold and ice. According to the passage, the adult penguins spend the winter south because   _  .
A. They have to raise their children there
B. they have to raise their chicks there
C. the food supply they need exists there
D. they have to give birth to chicks there
Answer: