凡身体患病不适宜游泳的人员可在人员陪同下下水训练。

阅读理解

     Every object has weight. But the center of its weight is not always in the middle of the object. If the

top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity(重力)

is high. But if the bottom is heavier, it won't fall easily. Then we say that its center of gravity is low.

     Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above

the line of its bottom (AB).

     Now look at the second picture. There are some heavy things in the bottom of this box. It will not fall,

because its center of gravity is above its bottom.

1. Box _____________will not fall..

2. The main idea of the passage is _________.

A. why things fall over  

B. a low center of gravity

C. a high center of gravity

D. that everything has weight

补写出下列名篇名句的空缺部分。

①泉水激石，____________；好鸟相鸣，____________。（吴均《与朱元思书》）

②好读书，____________；____________，便欣然忘食。（陶渊明《五柳先生传》）

③野芳发而幽香，____________，风霜高洁，____________，山间之四时也。（欧阳修《醉翁亭记》）

④潮平两岸阔，____________。____________，江春入旧年。（王湾《次北固山下》）

在牙体应用术语中，属外形高点的定义是

A．通过牙体中心的一条假想轴
B．牙体各轴面最突出的部分
C．牙冠上三面相交处成一点所成的角
D．牙与牙在邻面互相接触的部位
E．牙冠上两面相交处成一线，所成的角

接上题，随先生准备在未来向银行提前偿还部分贷款，则他应当在按月正常偿还贷款本息（　　　）提出。

A．3个月后

B．6个月后

C．12个月后

D．18个月后

一级消防员化学防护服无焰燃烧时间（）s。

A.≤10

B.≤20

C.≤40

D.≤30