_____youunderstandthisrule，you‘llhavenodifficultyindealingwithsuchproblems.
A、WhileD
once 意思是 “一旦 ”。while “ 当⋯⋯ 时候 ” ;though“虽然”;unless “除非 ” 。“一旦 你明白了这个规则，处理类似的问题就不困难了。 ”显然， d 符合句子意思的表达需要。
It ‘s_____my power to make final decision on the matter.
Children who are over-protected by their parents may become_____.
It seems as if the sun_____round the earth since it rises in the east and sets in the west.
_____youunderstandthisrule，you‘llhavenodifficultyindealingwithsuchproblems.
The driver pulled_____at the traffic lights.
