11. The government should invest in developing ____ tourism.
A. sustainable B. steady C. long-lasting D. constant
12. Watch leaky faucets, which can cause a ____ increase in the water bill.
A. significantly B. signified C. significant D. significance
13. Humans have destroyed numerous animal and plant ____ due to resource consumption.
A. environments B. resources C. ecosystems D. habitats
14. Even unused electronics can suck up energy so if you ____ rarely-used items, you can reduce energy consumption and your electric bill.
A. will unplug B. unplug C. can unplug D. unplugged
15. My teacher said that recycling was a classic way to help the environment, but not many people ____ exactly which items should be recycled.
A. had known B. know C. knew D. knowing
