题干
Old people need special care in winter, as they are very______ to sudden change of the weather.
A：sensitive
B：painful
C：attractive
D：familiar
答案(点此获取答案解析）
A
，现用水平细绳将木块1固定在左边的墙上，传送带按图示方向匀速运动，当三个木块达到平衡后，1、2两木块之间的距离是（ ）
