某同学在探究浮力大小跟什么因素有关系时，做了如图所示的实验。
图中的两个线圈，套在一根光滑的玻璃管上。导线柔软，可自由滑动。开关S闭合后，则（ ）
The shop owner suddenly stopped talking with his mouth ________ like a big “O”. It was the President Xi Jinping.
