A:①②
B:②④
C:②③
D:③④
在“验证力的平行四边形定则”的实验情况如图甲所示,其中A为固定橡皮筋的图钉,O为橡皮筋与细绳的结点,OB和OC为细绳.图乙是在白纸上根据实验结果画出的图.
Customers with a strong emotional investment in your company or brand will feel ____(背叛) if you ever let them down.
汉朝、宋朝和元朝加强中央集权的措施最相似的是