西晋王朝存在时间非常短暂。导致西晋是一个短命王朝的原因有（    ）

①统治集团迅速腐朽

②北方人大量迁往江南地区

③皇族之间连年混战

④内迁少数民族反抗西晋的压迫

阅读理解

    One of my best friends went abroad to enjoy her holidays, so the job of looking after her dog Missy has been given to me. A few months ago, Missy came to my friend's house. She looked terrible. She has been abused for a long time.

    When we first visited my friend and Missy, my friend had to gently pull her over on a lead (牵绳) to get her to come to us. She wanted to come but afraid to do so—the poor, beautiful thing. Clearly Missy came to the right home. My friend has given birth to a baby of his own and shows the love of a mother. This is just what Missy needs. Thanks to the love of my friend, she has changed into a new dog step by step. Sadly, she is still afraid of strange humans. I hate to imagine what the dog must have gone through.

    Now, Missy trusts me completely, so I can touch her berry（肚皮）.While standing, she will jump up so gently to be closer to me, putting her paws（爪子）on my legs as she looks at me with those beautiful eyes.

    Missy is really brave. She has the courage to try again, to open her hearts, and to know that not everyone is the same kind of people as before. Keep it in mind that tomorrow is another day.

I have four ruler.____ 改为____