Explanation: When a storage cell is charged from a fixed voltage source, its internal voltage (electromotive force, EMF) gradually increases as it accumulates charge. This internal cell voltage acts in opposition to the external charging voltage. As the cell's voltage rises, the *net* voltage driving the charging current into the cell decreases. This net voltage is the difference between the fixed external charging voltage and the cell's increasing internal voltage. According to Ohm's Law (I = V/R), if the effective voltage (V) across the internal resistance (R) of the charging circuit decreases, the charging current (I) will also decrease. Since the charging rate is directly proportional to the charging current, the rate slows down as the cell approaches full charge. Therefore, both statements A (cell voltage increasing, offering more opposition) and B (effective charging potential reducing, decreasing current) accurately describe why the charging rate decreases.