单项选择题
One needs a good sense of（） to ride a bike.
A.level B.skill C.balance D.ability
单项选择题 One day while Mr. King was working, he had a/an（）：his left leg was badly injured.
单项选择题 One cannot learn a foreign language well（）he studies hard.
单项选择题 One and a half hour（）since we arrive. No one has come to meet us.
