$1\mathrm{.}1$ How many select bits are used for the $4$:$1$ Mux?

$1\mathrm{.}2$ Which select bit is the most significant bit?

$1\mathrm{.}3$ Suppose S$1=1,$ S$0=0$ and $1$G $=0,$ then which signal will be assigned to output $1$Y$?$

$1\mathrm{.}4$ Now we still have S$1=1,$ S$0=0$ but $1$G $=1,$ then what will $1$Y be$?$

$1\mathrm{.}5$ Notice that we also have another set of inputs $2$D and output $2$Y$.$ Explain how $2$Y is related to

$2$D in one or two sentences.