Among the statements provided, the most accurate one regarding the ball-and-stick models used to represent the carbon cycle in the context of recycling carbon by plants is:
"Only the compounds that contain carbon should be shown in the cycle."
This statement emphasizes that the focus of the model is on carbon-containing compounds, which are integral to the carbon cycle, particularly in how carbon is taken up by plants during photosynthesis and later released through processes like respiration and decomposition.
Other statements may not accurately represent how the carbon cycle is visualized or the emphasis of the models typically used in educational contexts.