【多选题】保护接地和保护接零相比较有哪些不同之处 ()
A.
保护原理不同。低压系统保护接地的基本原理是限制漏电设备对地电压,使其不超过某一安全围高压系统的保护接地,除限制对地电压外,在某些情况下,还有促成系统中保护装置动作的作用。保护接零的主要作用是借接零线路使设备潜心电形成单相短路,促使线路上保护装置迅速动作。
B.
适用范围不同。保护接地适用于一般的低压不接地电网及采取其它安全措施的低压接地电网;保护接地也能用于高压不接地电网。不接地电网不必采用保护接零。
C.
线路结构不同。保护接地系统除相线外,只有保护地线。保护接零系统除相线外,必须有零线;必要时,保护零线要与工作零线分开;其重要地装置也应有地线。
【判断题】在公关调查中,随机抽样法是一种准备率高,但又省时、省力、省钱的好方法。()
【多选题】保护接地和保护接零相比较有哪些不同之处?
【多选题】Part II Reading Comprehension (2*20=40 points) Passage 1 The following are the story of Mary. Put A-E in the correct order .(2*5=10points) 下面是有关于 Mary 的故事,读内容,将 A-E 排序。 Mary had a really busy weekend...
A.
On Saturday morning, she played the piano.
B.
In the evening she went shopping with her mom.
C.
Mary felt a little bit tired and went to bed early on Sunday evening.
D.
Mary helped mom to do some cleaning on Sunday afternoon.
E.
She went to library with her friends on Sunday morning. 21 → 22 → 23 → 24 → 25
【单选题】She went on reading _____ it was midnight.
【判断题】在公共关系调查中,随机抽样法是一种准确率高,且又省时、省力、省钱的好方法。()
【单选题】提出的党在新形势下的强军目标是:建设一支听党指挥、能打胜仗、()的人民。
【简答题】根据以下提供的信息,填写Jessica的周末活动安排表。 Jessica had a busy weekend. She got up at 6:00 on Saturday morning. She had breadfast at 7:00. Then she borrowed some books from the library. In the afternoon, she played ...
【简答题】Fill in the blanks with proper words. murmur grunt mumble whisper mutter The man could only __________ an apology for the mistake he made. The child ____________ something in its sleep. He j...