21. When he was running after his brother, the boy lost his ___ and had a bad fall.
A
balance
B
.chance
C
.memory
D
.place
句意：男孩在追他哥哥时，失去平衡，重重地摔了一跤。A项“平衡”B项“机会”C项“记忆”D项“地方”。lose one’s balance“失去平衡”，故选A项。
从后面had a bad fall可知，摔跤之前应该是失去平衡。
对于固定搭配lose one’s balance的不熟悉。