The diagram shows a circuit containing three lamps and three switches ${S_1}$, ${S_2}$ and ${S_3}$.
Lamp 1 and lamp 3 are lit, but lamp 2 is not lit.
Which switch or switches is/are closed?

1 )
${S_1}$ only
2 )
${S_1}$ and ${S_2}$
${S_1}$ and ${S_3}$
4 )
${S_2}$ and ${S_3}$
تحلیل ویدئویی تست
تحلیل ویدئویی برای این تست ثبت نشده است!