已知甲苯的一氯代物有4种，则甲苯完全氢化后的环烷烃的一氯代物有( ) A.3种 B.4种 C.5种
My father, at the death of his father, was six years old, and he grew up without education. He moved from Kentucky to Indiana when I was seven. We reached our new home about the time the sta
如图所示，当高速公路收费站的栏杆升起时，它相当于 A．省力杠杆 B．费力打杆C．等臂杠杆
下列说法错误的是( ) 第11题图 A. 装置①可用于制二氧化碳 B. 装置②可用于制氧气 C. 装置③可用于收集二氧化碳 D. 装置④可用于收集氢气
下列设计方案可行，且化学方程式书写正确的是 A．用硫在盛空气的集气瓶中燃烧测定空气中氧气的含量： B．用适量的稀盐酸除去铁表面的锈迹：Fe2O
27. In the absence ____ necessary exercise, he can get ill easily. So he is often absent ___ class. A. for / in B. of / for C. of / from
利用细胞工程方法，以SARS病毒核衣壳蛋白为抗原制备出单克隆抗体。下列相关叙述正确的是 A．用纯化的核衣壳蛋白反复注射到小鼠体内，产生的血清
--What a hot day! How about going swimming after school? -- ! Let's ask Daniel to go with us． A．That's OK B．No problem C．Good luck
