Compare the productivities of a swamp and a river, and give two reasons for the difference

A swamp is an area of a land that is permanently filled with water. It could be formed out from a former lake or pond overtaken by trees. It is also dominated by trees. Cypress and tupelo trees, bushes and shrubs grow in swamps and even tiny plants like the duckweed that almost covers the water surface.
A river is a large area where water flows to the ocean, the lake, etc. and its seawater consistently evaporates. Its source could be from a melting snow, a melting glacier, a lake with an out-flowing stream or a spring bubbling out of the ground.

Two reasons for the difference:
1. Swamps have many formed marine animals and insects while the river, you can only rarely find one (like fishes).
2. Rivers could be a source of water into houses, farms and even a drinking water for humans while swamps could not be a source for those.

Your answer is b. codominant

Photosynthesis. . .