单项选择题 27、离心泵操作中，能导致泵出口压力过高的原因是（   ）。 A、润滑油不足 B、密封损坏 C、排出管路堵塞 D、冷却水不足

单项选择题 微分方程的图形称为微分方程的积分曲线.

单项选择题 The movie “Babel” referred to ____ A、expresses people’s ambition to explore the mystery of outer space. B、expresses the indifference and incomprehensibility among human being. C、describes the transformation of people from mental distance to mutual understanding, expresses people’s desire to communicate with each other.