Question $21$

A digital device processes electronic signals that represent either

a one $("$on$")$ or a two $("$off$").$

a one $("$on$")$ or a negative one $(-1$ for "off"$).$

a one $("$yes$")$ or a three $("$no$").$

a one $("$on$")$ or a zero $("$off$")$