请写出一个以直线 x=-2 为对称轴,且在对称轴左侧部分是上升的抛物线的表达式,这条抛物线的表达式可以是 。
y=-(x+2)2(答案不唯一)
— Is there any better way to help my son get rid of the habit of playing computer games?
— To tell you the truth, it's very hard. But we on this problem to improve the situation.[ ]
A. were working
B. had worked
C. are working
D. had been working
下列有关DNA二级结构特点的叙述,错误的是
A.两条多聚核苷酸链反向平行围绕同一中心轴构成双螺旋
B.以A-T以及G-C方式形成碱基配对
C.双链均为右手螺旋
D.链状骨架由脱氧核糖和碱基组成
E.维持双螺旋稳定的主要因素是氢键和碱基堆积力