怎样上步投掷垒球？

根据你的经历与理解，选择中 * * 的一个传统节日，写一段说明性文字。

要求：(1)说明顺序合理、清晰；(2)运用举例子、作比较的说明方法；(3)引用与之相关的一句古诗；（4)不少于200字。

如图所示，长度为L的轻绳上端固定在O点，下端系一质量为m的小球（小球的大小可以忽略）． 由图示位置无初速度释放小球，求当小球通过最低点时的速度大小及轻绳对小球的拉力．（不计空气阻力）

土壤水

非专职 * * 、副 * * 或者委员自任职之日起，其尚未履行的劳动合同期限短于任期的，劳动合同期限（）至（）。但是，任职期间个人严重过失或者达到法定退休年龄的除外。

A、自动延长，任期期满

B、自动中止，任职期间

C、自动延长，任职期间

D、自动延长，任职期满

Throughout history has (1) changed his physical environment in order to improve his (2) of life. With the tools of technology he has (3) many physical features of the earth. He has (4) woodlands and prairies into farms and made lakes and reservoirs (5) of rivers for irrigation purposes or hydroelectric (6) . Man has also modified the face of the earth by (7) marshes and cutting through mountains to (8) roads and railways.
However, man’s (9) to the physical environment have not always had beneficial results. Today, (10) of the air and water is an increasing danger to the health of the (11) . Each day thousands of tons of gases come out of the exhausts of motor vehicles. (12) from factories pollutes the air of industrialized areas and the surrounding (13) of the countryside. The pollution of water is equally harmful. The whole ecological (14) of the sea is being changed and (15) wastes have already made many rivers lifeless.
Now (16) protection is more pressing than ever before. As we know, massive destruction of the environment has brought about (17) effects and even poses a great (18) to man’s existence. Indifference to these problems will mean committing suicide. Therefore, effective (19) should be taken and laws passed to (20) the environment. Otherwise, man is certain to suffer from the serious consequences caused by this lack of care for his living surroundings.