单项选择题 属于化学性致病因素的是 A. 高温 B. 紫外线 C. 大气压 D. 芥子气

多项选择题 管道特征的路径线可以是（）A. 多段线，两两之间没限制B. 一段线C. 没有限制D. 多段线，但线必须两两相切

单项选择题 In this section, you will hear one passage. At the end of the passage, you will hear four questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D).A、Bricks. B、A mixture of rock and soil. C、Concrete. D、Steel.