开车过程中,乙烯精馏塔全回流运行,投用塔顶丙烯冷凝器应在()。
A.投用高压乙烯系统时
B.乙烯精馏塔接气相乙烯时
C.乙烯精馏塔接液相乙烯时
D.回流泵液相预冷时
参考答案:B
螺杆式压缩机正常停机待滑阀回到()时,按下主机停止按钮,压缩机停止运转。
A.0
B.10%
C.45%~50%
D.100%
Directions: For this part, you are allowed thirty minutes to write a composition on the topic: A Letter to the University President about the Canteen Service on Campus You should write at least 100 words, and base your composition on the outline given in Chinese below:假设你是李明,请你就本校食堂的状况给校长写一封信,内容应涉及食堂的饭菜质量、价格、环境、服务等,可以是表扬,可以是批评建议,也可以兼有而有之。