If you are alone and you stumble into quicksand，you should______.

Have you heard about new compact Discs? They're the latest invention from Sony. A CD consists of a piece of aluminium coated with transparent plastic，12 cms across，for producing sound.

It's similar to an ordinary record，except that it's read by a laser beam，and the information recorded on the aluminium is digital.

The makers claim that a CD can reproduce the original sound perfectly，without any distortion or background hiss. As the system is computerized，there's no loss of quality between the studio master and the record you buy.

Also，a CD is much tougher-than a vinyl(乙烯基)record，so it doesn't need such careful handling. Dust and dirt won't damage it，and as there's no contact between the laser and the disc, it will never wear out.

随着研究技术的日益先进，用于实验的动物的数量可能会减少。

反对者认为病人并不一定真正希望结束生命，可能请求之后另有请求。

科学家们正致力于研究预报地震何时何地发生的计划。

他相信某些植物物种正受到灭绝的威胁。

在她死亡前，她没让歹徒知道，偷偷把微型录音带放进了自己的衣袋里。

They removed personal items-bags，notebooks，her six-year-old son's ______(belong)from the car.

It is imperative that the students______(finish)writing their papers before July lst.

The pioneer type was the characteristic one at the turn of the seventeenth century and also fit the beginning of the______(twenty)century，but it is much less evident today.

 Every worker has a highly developed sense of how much work______(expect)of him.