Read the following passage and circle the letter A, B, C, or D to indicate the correct word or phrase that best fits each of the numbers blanks.
① Our future house will be on the ocean. It will be surrounded by tall trees and a blue sea. But we only have salt water in the ocean. We need fresh water for ___(1)___ and for growing food ___(2)___ farms. Ocean water is too salty to drink. It is also too salty for watering plants. We must have ___(3)___ to make ___(4)___ water from salty water. We should be ___(5)___ not to waste water.