如图电路中,当S1闭合、S2断开时,电压表的示数为2.5V;当S1断开、S2闭合时,电压表示数为6V,则灯L1两端电压为____V,灯L2两端的电压为____V,电源电压为____V.
Can students ____ (eat) in the hallways?