Mammals can be divided into two groups: marsupials and placentals. although both groups are mammals, there are several features that distinguish the two groups. one of the biggest differences between marsupials and placentals is the gestation and nurturing periods and process of each group. essentially, marsupials spend significantly more time nursing and caring for their young after birth than placentals. placentals, on the other hand invest more time and energy in pregnancy. this has led many biologists to speculate that marsupials are inferior to placentals for a variety of reasons.
Marsupial offspring spend a significant portion of their developing period in the abdominal pouch of their mother. this leads to slower development of specific organs and body systems compared with placental mammals. most critically, immune systems of marsupials young are neither given sufficient time to develop, nor are they given sufficient time to be introduced to maternal antigens which stimulate the production of helpful antibodies. this compromised and underdeveloped immune system puts marsupials at risk and is evidence of their inferiority.
Some marsupials lack certain abilities that allow them to adapt to the surrounding environment. for example, the joey, a small marsupial, is unable to regulate its own body temperature and relies on external heat sources. for this reason, the mother must carry the young joey in her pouch to keep it warm until it develops fur as an adult this weakness in survivability opens up both the carrying mother and the young joey to danger.
Marsupials have also demonstrated their inability to compete with placentals. in almost all the ecosystems in which marsupials exist, marsupial species have been in a steady decline to placental species which, on the other hand, have demonstrated robust and steady population growth. this trend speaks to the inability of marsupials to adequately compete for resources and niche environments.
综合写作音频：
Your professor is teaching a class on education.Write a post responding to the professor’s question.
In your response, you should do the following.
Express and support your opinion.
Make a contribution to the discussion inyour own words.
An effective response will contain at least 100words.
Doctor Achebe
Companies now make computer games designedto help very young children learn. The games areadvertised for use by children aged 2 to 8 yearsand often involve basic math and reading skills,presented in a fun, game-like style. Some peoplesay that this results in children spending too muchtime looking at computer screens. Do you think it’sa good idea for very young children to play
educational computer games? Why or why not?
Andrew
I think it’s completelyinappropriate for children as young as 2years old to play what are essentially video games. Even if thegames are educational, the same skills can be taught intraditional ways-by reading books to children, for example.And it would be beneficial to interact with their parents in thisway.
Kelly
Considering how important computers are to human societiesthese days, l think it actually makes sense to allow very youngchildren to explore them. And if the computer games thatchildren play also give them early access to subject matterthat will later be taught in school, all the better.
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