用你喜欢的方法计算．

命题“$\exists x\in Z$，x²＋x＋m＜0”的否定是（    ）

读书是有益的，但人却不可因为“书”而框住手脚。我们应懂得（    ）

①与认识相比，实践是第一位的

②认识不过是一种圆圈式的循环运动

③解放思想要打破一切现存的东西

④坚持革命批判精神是十分重要的

根据短文内容选择正确答案。

      A well-known old man was being interviewed and was asked if it was correct that he had just celebrated his ninety-ninth birthday.

     “That's right.” said the old man. “Ninety-nine years old, and I haven't an enemy in the world. They're all dead.”

  “Well, sir,” said the interviewer, “I hope very much to have the honour of interviewing you on your hundredth birthday.”

     The old man looked at the young man closely, and said, “I can't see why you shouldn't look fit and healthy to me!”