如图所示，M、N和P是以MN为直径的半圆弧上的三点，O点为半圆弧的圆心，∠NOP=90°。电荷量相等、电性相反的两个点电荷分别置于M、N两点，这时O点电场强度的大小为E₁；若将N处的点电荷移到P点，则O点的电场强度大小变为E₂则E₁与E₂之比为

A．1:2

B．：1

C．2：1

D．1：

Upon underwater detection, there were no apparent defects on the bottom plates, bilge keels,rudder and propeller of the said vessel. This kind of wording usually appeared on（）.

A.ship surveyor's report

B.a ship's certificate

C.a cargo inspection report

D.a dive survey report