Explanation:
The student most likely observed both (A) Vacuole and (C) Chloroplast that led him to the conclusion, that the cell is a plan cell.
Reason :
In a plant cell, Vacuole occupies 70% to 90% of the total volume of the cell, making it easier to identify.
Chloroplast contains photosynthetic pigment called chlorophyll (green in colour), which is only found in plant cell.