A:Don’t worry
B:Of course
C:A piece of cake
D:Never mind
如图,一光滑的轻滑轮用细绳OO′悬挂于O点;另一细绳跨过滑轮,其一端悬挂物块a,另一端系一位于水平粗糙桌面上的物块b.外力F向右上方拉b,整个系统处于静止状态.若F方向不变,大小在一定范围内变化,物块b仍始终保持静止,则( )
顺次连接对角线互相垂直的四边形的各边中点,所得图形一定是 ( )
根据问句,选择最佳答案。
① Good morning. ____ A. Good morning.
② What do you see? ____ B. Yes, I like sweets.
③ Do you like sweets? ____ C. It's sunny.
④ What do you hear?____ D. I see a bee
⑤ How's the weather?____ E. I hear a sheep.
组成肺的最小的结构和功能单位是____、