A:①→②→③
B:③→②→①
C:②→③→①
D:③→①→②
用四只完全相同的滑轮和两根相同的绳子组成如图所示的甲、乙两个滑轮组,不计绳重和摩擦,则下列说法正确的是()
When she knew her son was out of danger, she was relaxed.