Even if we learn something well, we will forget it ______ we use it.
句意：即使我们学得很好，除非我们使用它，否则我们也会忘记。
考查unless引导的条件状语从句。while当……时；until直到；unless除非。分析句子可知，此处表示“即使我们学得很好，除非我们使用它，否则我们也会忘记”的含义，是unless引导的条件状语从句，强调“除非”，其他两项语意不通。故选C。
Even if we learn something well, we will forget it ______ we use it.
Wash your hands before meals, ______ you may get ill.
—Who went to the graduation party last night, Mary?
—Almost everyone did. ______ lots of students _____ Ms. Wang appeared at the party.
Restaurants must stop offering free plastic bags in Beijing _______ customers ask for them.
—Tim, our foreign teacher Ms. Green will go back to England next week.
—Really? Let's have a party to say goodbye to her ______ she is free this weekend.
______ you keep moving, you'll never reach the top of the mountain.
—Do you know the traffic rules?
—Sure, one of them is that we can’t go across the street _____ the light is green.
I waited ______ they finished talking.
Get up early, ______ you will miss your train.
Nobody can hear you ______you speak in a louder voice.
