The correct answer is B) 10 volts. In a parallel circuit, the voltage drop across each branch is the same as the source voltage. Since the resistors R1, R2, and R3 all have the same resistance of 10 ohms, the voltage drop across each branch will be 10 volts (30 volts divided by 3 branches). The other options are incorrect because: A) 5 volts is too low, as the voltage drop across each parallel branch would be the same as the source voltage of 30 volts divided by the number of branches (3). C) 20 volts is too high, as the voltage drop across each parallel branch would be the same as the source voltage of 30 volts divided by the number of branches (3). D) 30 volts is the full source voltage, which would not be the voltage drop across the parallel branches.