A. MUST B. CAN C. COULD D. MIGHTB. READ THE PASSAGE AND CHOOSE...

23. A. must B. can C. could D. mightB. Read the passage and choose the best answer for each question.Scientists often divide resources into two groups: renewable and non-renewable. When aresource is used, it takes some times to replace it. If the resource can be replaced quickly and easily,it is called renewable. If it cannot be replaced quickly and easily, it is non-renewable. All fossil fuelsare non-renewable resources. Solar energy, air, and water are usually called renewable because thereis an unlimited supply.However, this definition may change if people are not careful with these resources. The amountof solar energy that reaches the earth depends on the atmosphere. If the atmosphere is polluted, thesolar energy that reaches the earth may be dangerous. If humans continue to pollute the air, it willnot contain the correct amounts of these gases.Many resources are limited and non-renewable, and many are in danger of pollution. As aconsequence, resources must be conserved and the environment protected. Conservation mustbecome an important part of everyone’s life.