Water plants provide ....... to water animals.

Complete the following model of the carbon cycle by filling in $A, B, C, D, E,$ and $F$.

How many of the following organisms are decomposers in a pond ecosystem?
Some algae,fungi,bacteria,floating plants,submerged plants,flagellates.

Some of the stages in the hydrarch succession are labelled as:
$I.$ Marsh meadow stage
$II.$ Reed swamp stage
$III.$ Submerged plant stage
$IV.$ Phytoplankton stage
$V.$ Submerged free floating plant stage
Identify the choice that represents the correct sequence of these stages.

The world's most problematic aquatic weed is

Identify $X$ from the figure: