题目内容

当系统的流量增大时,油缸的运动速度就( )。

A. 变快
B. 变慢
C. 没有变化
D. 先快后慢

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减压阀控制的是( )处的压力。

A. 进油口
B. 出油口
C. A 和 B 都不是
D. C、A 和 B 都是

已知某液压泵的转速为 950r/min ，排量为 VP=168mL/r ，在额定压力 29.5MPa 和同样转速下，测得的实际流量为 150L/min ，额定工况下的总效率为 0.87，求：（1）液压泵的理论流量 qt；（2）液压泵的容积效率 η v；（3）液压泵的机械效率 η m；（4）在额定工况下，驱动液压泵的电动机功率 Pi；（5）驱动泵的转矩 T。

#创建数据库create database lx;use lx;#创建数据表CREATE TABLE students(sno VARCHAR(3) ,sname VARCHAR(4) NOT NULL,ssex VARCHAR(2) NOT NULL,sbirthday DATETIME,class VARCHAR(5));CREATE TABLE courses(cno VARCHAR(5),cname VARCHAR(10) NOT NULL,tno VARCHAR(10) NOT NULL);CREATE TABLE scores(sno VARCHAR(3) ,cno VARCHAR(5) NOT NULL,degree decimal(10, 1) NOT NULL);CREATE TABLE teachers(tno VARCHAR(3) ,tname VARCHAR(4) NOT NULL, tsex VARCHAR(2) NOT NULL,tbirthday DATETIME NOT NULL, prof VARCHAR(6),depart VARCHAR(10) NOT NULL);#插入数据INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (108 ,'曾华' ,'男' ,'1977-09-01',95033);INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (105 ,'匡明' ,'男' ,'1975-10-02',95031);INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (107 ,'王丽' ,'女' ,'1976-01-23',95033);INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (101 ,'李军' ,'男' ,'1976-02-20',95033);INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (109 ,'王芳' ,'女' ,'1975-02-10',95031);INSERT INTO STUDENTS (SNO,SNAME,SSEX,SBIRTHDAY,CLASS) VALUES (103 ,'陆君' ,'男' ,'1974-06-03',95031);INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('3-105' ,'计算机导论',825);INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('3-245' ,'操作系统' ,804);INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('6-166' ,'数字电路' ,856);INSERT INTO COURSES(CNO,CNAME,TNO)VALUES ('9-888' ,'高等数学' ,100);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (103,'3-245',86);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (105,'3-245',75);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (109,'3-245',68);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (103,'3-105',92);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (105,'3-105',88);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (109,'3-105',76);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (101,'3-105',64);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (107,'3-105',91);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (108,'3-105',78);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (101,'6-166',85);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (107,'6-106',79);INSERT INTO SCORES(SNO,CNO,DEGREE)VALUES (108,'6-166',81);INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (804,'李诚','男','1958-12-02','副教授','计算机系');INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (856,'张旭','男','1969-03-12','讲师','电子工程系');INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (825,'王萍','女','1972-05-05','助教','计算机系');INSERT INTO TEACHERS(TNO,TNAME,TSEX,TBIRTHDAY,PROF,DEPART) VALUES (831,'刘冰','女','1977-08-14','助教','电子工程系');create table grade(low int(3),upp int(3),rank char(1));insert into grade values(90,100,'A');insert into grade values(80,89,'B');insert into grade values(70,79,'C');insert into grade values(60,69,'D');insert into grade values(0,59,'E');简单描述上面的sql命令完成了什么操作？

查询所有“女”教师和“女”同学的name、sex和birthday.（合并查询结果）