Explanation: For the voltage drop across R1 to be 9 volts, R1 must be connected directly across the 9-volt power source. According to basic circuit theory, specifically Kirchhoff's Voltage Law, if R1 is the only component in a simple series circuit with a 9V source, all 9 volts are dropped across R1. Alternatively, if R1 is connected in parallel with other components, and this parallel combination is placed directly across the 9-volt source, the voltage drop across R1 (and all components in parallel with it) will also be equal to the source voltage. The other options (1.2V, 2.4V, 3.7V) would only be correct if R1 were part of a voltage divider or another series-parallel circuit where the voltage was distributed among multiple series components. Since the full 9 volts are dropped across R1, it implies R1 is directly across the source.