In the circuit shown in the figure, the power supply voltage remains unchanged. When the switch S1 is closed, the lamp l will light up. If the switch S2 is closed again, then () A. The number of two ammeters increases B. the brightness of light l decreases C. The total resistance of the circuit decreases D. the number of voltmeters increases

In the circuit shown in the figure, the power supply voltage remains unchanged. When the switch S1 is closed, the lamp l will light up. If the switch S2 is closed again, then () A. The number of two ammeters increases B. the brightness of light l decreases C. The total resistance of the circuit decreases D. the number of voltmeters increases

When the switches are all closed, it is a parallel circuit, so the branch current remains unchanged and the total current becomes larger, so option a is incorrect; because the branch current remains unchanged, the brightness of lamp L remains unchanged, so option B is incorrect; in the parallel circuit, the more branches, the smaller the total resistance, so option C is correct; the voltage at both ends of the parallel circuit remains unchanged, so the voltage expression remains unchanged; so option C is selected