In this section, you will hear one passage. At the end of the passage, you will hear four questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D).A、By containers made by concrete.
B、By containers made by steel.
C、By using reservoirs formed by dirt walls.
D、By using reservoirs formed by wood.