1) If we don’t reduce plastic waste, sea animals _______ mistake it for food. a) must b) should c) could 2) Scientists say the temperature _______ rise faster than expected this decade. a) could have b) may c) shouldn't 3) If communities plant more trees, the air quality _______ improve quickly. a) might b) couldn't c) might not 4) Heavy pollution from the factory _______ be the reason for the strange smell near the river. a) could b) should c) must 5) If we switch to solar energy, electricity costs _______ become much lower in the future. a) should b) need c) could 6) . You _______ recycle glass and paper in this city—it’s the law a) musn't b) have to c) must 7) People _______ use their cars every day; walking or cycling is enough. a) don't have to b) mustn't c) should 8) Factories _______ follow strict rules to reduce the amount of smoke they produce. a) needn't b) have to c) should 9) We _______ waste water when there is a drought; there will be other problems if we don't act now. a) needn't b) musn't c) shouldn't 10) You _______ bring your own bags to the supermarket if you want, but it’s a good idea. a) don't have to  b) should c) must 11) The river is very polluted today. The factory _______ (must) dumped chemicals last night. a) must have b) could have  c) must 12) The government _______ (should) acted earlier to protect the endangered birds. a) could have b) should c) should have 13) The strange noise in the forest _______ (might) been a wild animal. a) might b) might not have c) might have 14) The fish died suddenly; the water _______ (can’t) been safe. a) can not b) can't have c) couldn't have 15) We _______ (could) saved more energy last winter if we had used better insulation. a) could b) could have c) should have

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