①如图甲：把正在发生的音叉靠近悬挂的静止乒乓球，看到乒乓球被反复弹起；
②如图乙：把正在响铃的闹钟放在玻璃钟罩内，逐渐抽出其中空气，发现铃声明显减小；
③如图丙：拨动同一把钢尺，在保证其振幅相同情况下，改变其伸出桌边的长度，观察钢尺振动的快慢．
Hello, everyone! I'm Kathy. I live in Washington, D.C. I'm in Grade 8. I spend about half an hour on my homework every day. My homework this week is to find out how much homework students have now. Please tell me about your homework on the website.
如图，△ABC，△EFG均是边长为2的等边三角形，点D是边BC、EF的中点，直线AG、FC相交于点M．当△EFG绕点D旋转时，线段BM长的最小值是（ ）
— _________ they are very cute.
