员工遵纪守法，必须做到 () A．有法可依 B．反对“管、卡、压” C．执法必严 D

设{a_n}是正项等差数列，{b_n}是正项等比数列，且a₁=b₁，a_2n+1=b_2n+1则[ ]

A．a_n+1=b_n+1

B．a_n+1≥b_n+1

C．a_n+1≤b_n+₁

D．a_n+₁＜b_n+1

如图所示，在做“寻找等效力”的实验中，在水平放置的木板上垫一张白纸，把橡皮条的一端固定在A点上，另一端连接两根细线，然后通过细线用两个互成角度的弹簧秤来拉橡皮条，使橡皮条的结点拉到某一点O，记录两弹簧秤的读数和两细线的方向以及结点O的位置；然后改用一个弹簧秤把橡皮条的结点再次拉到O点，记录弹簧秤的读数和细线的方向.请问：为什么两次要将结点拉到同一位置？（　　）

A．这样可以方便作图

B．其实两次结点不是拉至同一位置也可以

C．这样做可保证两次弹簧的伸长量相同

D．这样做可保证两次力的作用效果相同

About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along free on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course. The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen.
The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoots withorganic nitrogen compounds. This comes in handy for the growth of buds in the early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can "export" protein to the rest of the plant in the form of amino acids.

Which of the following best describes the organization of the passage

A．The results of two experiments are compared.

B．A generalization is made, and several examples of it are given.

C．The findings of an experiment are explained.

D．A hypothesis is presented, and several means of proving it are suggeste

实验室应使用适合的方法和程序进行所有检测和(或)校准，包括被检测和(或)校准物品的抽样、处理、运输、存储和准备。适当时，还应包括测量不确定度的评价和分析检测，和(或)校准数据的统计技术。( )

隐身技术代表了现代伪装技术的一个发展方向。