Possible answers:
(1). pH.
(2). rocks.
(3). soil.
(4). sand.
(5). crust.
(6). Joules.
(7). salt.
(8). dirt.

Fact 1: When a river floods , that river deposits soil in flood plains. Fact 2: Rivers become silted, plains flooded. Given the two facts above, what do rivers deposit when they flood?
Answer:
(3).