(A)

No. 11

1 It is located on top of freshwater rivers.

2 It can be dangerous for divers who enter it.

3 It occurs where fresh water and salt water meet.

4 It is the saltiest part of the caves’ water.

No. 12

1 They require more sunlight than once thought.

2 They rely heavily on plant material for food.

3 They drain oxygen from the environment.

4 They may provide an alternative source of food energy.