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The population problem may be the ___1___ one of the world today. The world’s population is growing ___2__ . Two thousand years ago, there were only 250 million people ___3___ the earth. Four hundred years ago, the number was __4__ 500 million.
The population problem may be the ___1___ one of the world today. The world’s population is growing ___2__ . Two thousand years ago, there were only 250 million people ___3___ the earth. Four hundred years ago, the number was __4__ 500 million.
