制动零部件外部清洗或烘干的最高温度不高于（）。 A.30° B. 40° C. 50

如图所示，在场强大小为E的匀强电场中，一根不可伸长的绝缘细线一端拴一个质量为m电荷量为q的带负电小球，另一端固定在O点．把小球拉到使细线水平的位置A，然后将小球由静止释放，小球沿弧线运动到细线与水平成θ=60°的位置B时速度为零．以下说法正确的是（　　）

A．小球重力与电场力的关系是mg=

3

Eq

B．小球重力与电场力的关系是Eq=

3

mg

C．球在B点时，细线拉力为T=

3

mg

D．球在B点时，细线拉力为T=2Eq

如果把增加2kg记作+2kg，那么减少7kg记作（    ）kg。

有一台三相配电变压器,额定容量为800kVA,变压比为10kv／0.4kV,试计算高 压侧的额定电流。 若在高压侧选用50／5的电流互感器，试计算当高压侧为额定电流时，流过继电器 的电流Ij=多少A

The most popular organic gem is the pearl. A pearl is the response of a marine mollusk to the presence of an irritating impurity accidentally introduced into its body; a cultured pearl is the result of the intentional insertion of a mother-of-pearl bead into a live mollusk. Whether introduced accidentally or intentionally, the pearl-making process is the same: the mollusk coats the irritant with a substance called nacre. Nacre is composed chiefly of calcium carbonate. Because very few natural pearls are now on the market, most pearls used in free jewelry are cultured. These include "Biwa" pearls and most other freshwater pearls. Cultured pearls are not easily distinguished from natural pearls except by an expert.

What is the chief component of nacre

A．Sand.

B．Bead.

C．Calcium carbonate.

D．Biwa.

在高速公路上遇分流交通管制时，可不驶出高速公路，就地靠边停靠等待管制结束后继续前行。