以下哪条命令可以改变文件file的所有者为Sam()?A.chmod Sam fileB.chown Sam fileC.chgrp Sam fileD.umask Sam file

中央分隔带的波形梁护栏和混凝土护栏的防护等级为（ ）。

A.Bm、Am、SBm、SAm、SSm 五级
B.Cm、Bm、Am、SBm、SAm、SSm 六级
C.Bm、Am、SBm、SAm、SSm、HBm 六级
D.Bm、Am、SBm、SAm、SSm、HBm、HAm 七级

设置于中央分隔带的护栏分为（ ）。

A.SAm、SBm、Am三级
B.Am、SBm、SAm三级
C.A、B、SA、SB、SS五级
D.Bm、Am、SBm、SAm、SSm、HBm、HAm七级

C
Uncle Sam is a tall，thin man.He‘s an older man with white hair and a white beard.He often wears a tall hat，a bow tie，and the stars and stripes of the American flag.
Who is this strange，looking man Would you believe that Uncle Sam is the US government But why do you call the US government Uncle Sam
During the War of 1812，the US government hired meat packers to provide meat to the army.One of these meat packers was a man named Samuel Wilson.Samuel was a friendly and fair man.Everyone liked him and called him Uncle Sam.
Sam Wilson stamped the boxes of meat for the army with a large US for United States.Some government inspectors came to look over Sam‘s company.They asked a worker what the US on the boxes stood for.As a joke，the worker answered that these letters stood for the name of his boss，Uncle Sam.
The joke spread，and soldiers began saying that their food came from Uncle Sam.Before long，people called all things that came from the government“Uncle Sam‘s”，“Uncle Sam”became a nickname for the US government.
Soon there were drawings and cartoons of Uncle Sam in newspapers.In these early pictures，Uncle Sam was a young man.He wore stars and stripes，but his hair was dark and he had not a beard.The beard was added when Abraham Lincoln was President.President Lincoln had a beard.
The most famous picture of Uncle Sam is on a poster from World War I.The government needed men to fight in the war.In the poster，a very serious Uncle Sam points his finger and says“I want YOU for the US Army.”
“Uncle Sam”became a________for the US government.

A.boss
B.nickname
C.picture
D.businessmen