Which of the following actually prevents dirt and leaves from falling inside the tank

A．The two bags holding the water should be put inside the metal tank.
B．The inner bags need to be replaced every two years.
C．The water harvesting system should be built on a platform.
D．A cover should be used to prevent insects from eating it.

A．The research indicates that most students with only one Jewish parent will not think themselves as Jewish.
B．The survey was carried out among Jewish Freshmen.
C．The research survey didn't find out what and how these Jewish students think about their religion.
D．The research presents a new perspective for the future study.