Answer
Ammeter readings, greatest to least: C, B, A.
Work Step by Step
The bulbs are in parallel, and have the same voltage across them, identical to the battery voltage.
Because the bulbs are identical, and the voltages are the same, the current through each is identical.
In a simple parallel circuit, the sum of the branch currents add up to the total current supplied by and flowing through the voltage source.
This is Rule 3 for parallel circuits, on page 444, and discussed on pages 443-444. This is also illustrated in Figure 23.18.
The battery in case B supplies twice the current as the battery in case A.
The battery in case C supplies three times the current as the battery in case A.
