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【单选题】
下列命题不正确的是（）。A.
平面上到两定点的距离之和为定长（大于两定点间的距离）的动点轨迹是椭圆
B.
平面上到定点与定直线距离之比为常数p且0
C.
平面与圆锥的交线是椭圆
D.
满足方程 （a>b>0）的平面曲线是椭圆
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【单选题】We can infer from the passage that the oldest form. of communication between people is ______.
A.
speech
B.
touch and hearing
C.
sounds
D.
body language
【单选题】下列关于双代号网络图和单代号网络图的表述，正确的是()。
A.
双代号网络图又称节点式网络图
B.
双代号网络图是以箭线及其两端节点的编号表示工作
C.
单代号网络图又称箭线式网络图
D.
单代号网络图的节点表示工作的开始或结束以及工作之间的连接状态
【简答题】Barter trade is the oldest form of trade, which is a direct exchange of one goods for another deemed to be of approximately equivalent value without any flow of money taking place. It is a primitive w...
【单选题】Water is the oldest form. of transport. The original sailing vessels were replaced by steamboats in the early 1800s and by diesel power in the 1920s. A distinction is generally made between deepwater ...
A.
Steamboats are the original sailing vessels.
B.
Steam power followed diesel power.
C.
Deepwater and navigable inland water transport are equivalents.
D.
There is domestic commerce in the Atlantic Ocean.
【单选题】we can infer from the passage that the oldest form. of communication between people is ______.
A.
speech
B.
touch and hearing
C.
sounds
D.
body language
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