The observation that sugar crystals collect at the bottom of the iced tea solution occurs because the solution has reached its saturation point. In this context, the following statement best accounts for the observation:
"When the solution becomes saturated, it can no longer dissolve any more sugar, so any additional sugar added remains undissolved and collects at the bottom."
In other words, a saturated solution is one where the maximum amount of solute (sugar) has been dissolved in the solvent (iced tea) at a given temperature. Once the saturation point is reached, any excess solute will not dissolve and will settle out.