碳氢化合物是大气污染物之一，下列现象的产生与碳氢化合物有关的是A．臭氧空洞 B．酸雨 C．温室效应 D．光化学烟雾
“神农耕而作陶”反映的历史现象是 A．半坡原始居民过着以农耕为主的定居生活 B．大汶口墓葬中有大量陶器随葬品 C．原始农业的发展促进了
As little children，most of us were taught the virtue of honesty from fairy tales and other stories. The story of Pinocchio, who begins life as a puppet, teaches us the ___36__of telling the truth.
下列与染色体变异有关的说法中不正确的是 A．染色体变异包括染色体结构的改变和染色体数目的改变 B．两条染色体相互交换片段引起的变异属于染色
地球上最大的生态系统是 ，它是所有生物的共同家园。
The students competed____ the honor of winning ____ each other ____ the school sports meet. A. for, against, in B. in, with, against C. against, for, at
In the early 1800’s, a boy named John lived in an orphanage (孤儿院) with several other children. Every day was 36 working and Christmas was the one day of the year 37 the children did no
（1）张明同学要用伏安法测定一太阳能电池E1的电动势和内阻（电动势约2V，内阻约50，允许通过的最大电流为400mA）。除了待测电池、开关和若干导线
