①互补碱基对之间氢键断裂      

②互补碱基对之间氢键合成

③DNA分子在解旋酶的作用下解旋 

④以解旋后的母链为模板进行碱基互补配对

⑤子链与母链盘旋成双螺旋结构

根据对话内容,从方框内的选项中选出能填入空白处的最佳选项,其中有两个为多余选

A: Did you hear about the flood in Wuhan last night?

B: No. ____

A: My e-friend Lin Tao told me about it.It rained for a long time.

B:  ____

A: For about two weeks.

B:  ____

A: Yes, it was very terrible.There was water all around his house. Most of his furniture and his books get wet.

B:  ____ Did your e—friend still live in his house?

A: No. ____ There was no flood there because his uncle lives far away.

A. Oh, really?

B. That sounded bad.

C. He and his family moved to his uncle's house.

D. What happened?

E. How long did the rain last?

F. That sounded great.

G. That's all right.

某探究小组设计了“用一把尺子测定动摩擦因数”的实验方案．如图示，将一个小球和一个滑块用细绳连接，跨在斜面上端．开始时小球和滑块均静止，剪短细绳后，小球自由下落，滑块沿斜面下滑，可先后听到小球落地和滑块撞击挡板的声音，保持小球和滑块释放的位置不变，调整挡板位置，重复以上操作，直到能同时听到小球落地和滑块撞击挡板的声音．用刻度尺测出小球下落的高度H、滑块释放点与挡板处的高度差h和沿斜面运动的位移x．（空气阻力对本实验的影响可以忽略）

①滑块沿斜面运动的加速度与重力加速度的比值为____．

②滑块与斜面间的动摩擦因数为____．

③以下能引起实验误差的是____．

a．滑块的质量               b．当地重力加速度的大小

c．长度测量时的读数误差      d．小球落地和滑块撞击挡板不同时．