Please label all answers clearly

Question $2\mathrm{.}1.($ELECTRICIAN TOOLS$)$ A system of four relays of low standard was designed to run a drill as shown in the following figure:

Relays $R_1$ and $R_2$ are connected in parallel, so that subsystem functions correctly if either relay $R_1$ or $R_2$ functions. The relays $R_3$ and $R_4$ are connected in series, so that their subsystem works only if both relays work correctly.

$($a$)$ If all relays work independently of one another and $P($a given relay works