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【单选题】
下列关于多普勒描述错误的是（）.A.
PRF是Pulsed Repetition Frequency的缩写，也就是脉冲重复频率
B.
1/2PRF称为斯特频率极限）。如果血流速度过高，使多普勒频移超过1/2PRF，则会出现频率失真（混叠）
C.
CDFI，即彩色多普勒血流图，可以显示血流的方向
D.
CDE即彩色多普勒能量图，又称为CPA，可检测低流量、低流速血流
E.
CDE显示血流时也有混叠现象
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【多选题】Unless measures are taken at once, there is a possibility that all the oceans of the world will be dead by the next century. How can this possibly happen? We have already seen that people 【 C1 】 _____...
A.
limitations
B.
seashores
C.
allow
D.
invade
E.
close
F.
poisonous
G.
afterwards
H.
agenda
I.
edit
J.
figure K. impossible L. alone M. effects N. calculate O. extensive
【简答题】A new law has recently been announced which forbids people to disturb, annoy, harm, kill or interfere with any bats which choose to live in their houses. Anyone who disturbs a bat on its nest ,or hand...
【简答题】Revise the following sentences, omitting needless words . 1.Zhao was the person who was elected the representative of the class by the whole class. 2.Permit me to take this opportunity to inform you t...
【简答题】People are by law to obey the traffic rules.
【单选题】What are institutions required to do by a California law?
A.
Take new security measures.
B.
Write detailed reports.
C.
Catch hackers.
D.
Inform. the affected people that their personal information has been stolen.
【单选题】如下哪一项可作为管内流体流动流向判据？（）
A.
流体从总势能高处向总势能低处流动
B.
流体从压强高处向压强低处流动
C.
流体从位能高处向位能低处流动
D.
流体从动能高处向动能低处流动
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