foot的復數形式是什么

　　例句：

　　1.She stamped her foot again.

　　她又跺了跺腳。

　　2.David called to the children from the foot of the stairs。

　　戴維在樓梯下面喊孩子們。

　　3.Friends stood at the foot of the bed, looking at her with serious faces.

　　朋友們站在床腳處，神情嚴肅地看著她。

　　4.I tried to reach the foot brakes but I couldn't.

　　我試圖去夠腳剎，但是沒能踩到。