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Dave:
How many times do you brush your teeth every day,David? 
你一天刷几次牙，大卫？
David:
Once.
一次。
Dave:
No wonder you often get a toothache,brush your teeth twice a day and don't eat too much candy.
难怪你老是牙疼。一天刷两次牙，还有别吃太多糖果。
David:
OK,I will.
好，我会的。