請依下文回答第46題至第50題：       Is there any immortal creature in the world? Despite only being only three millimeters in diameter on average, adultversions of immortal jellyfish (Turritopsis dohrnii) have a huge party trick: they can roll back their biological clock wheninjured or on the verge of starvation. This means, in theory, they could live forever. Could humans harness their abilitiesto eradicate ageing completely?       As scientists have known, the reason of human ageing is a process called trans-differentiation. “This is about how afully formed specialized adult cell can become another type of specialized adult cell. It’s how a cell can adapt,” explainsDr. Maria Pia Miglietta. The exact mechanism behind trans-differentiation is still a mystery to scientists. However, asMiglietta explains, the answer will likely be found in the jellyfish’s genes. “It most certainly has something to do withthe DNA,” she says. “It’s the DNA that programs a cell––certain genes being ‘turned on’ or ‘off’ will determine whatsort of cell it is. We’re far away from any kind of real-world application,” says Miglietta. “But we hope that studyingwhat happens in these jellyfish can tell us how their genes change cells––and how these changed cells integrate withothers. This is the base of understanding cellular regeneration and tissue regeneration.”       However, there are many challenges. These jellyfish have only been studied sporadically since the early 1980s,meaning experts have only a few decades’ worth of data. While an immortal jellyfish can age in reverse, it can also beeasily killed by predators including various fish, sharks, turtles and even other jellyfish. “They’re incredibly sensitive,from the water temperature to their plankton and fish egg diet,” says Miglietta. “The real paradox is they’re actuallyreally hard to keep alive!”
【題組】46 What is the main idea of the passage?
(A)An endangered species that needs more conservation.
(B)A species that may help on research against ageing.
(C)The concept of human ageing and its solution.
(D)Biological background of jellyfishes reproduction.