Consider the methods used by processes P$1$ and P$2$ for accessing their critical sections whenever needed, as given below. The initial values of shared boolean variables S$1$ and S$2$ are randomly assigned. $($GATE $2010)$ Method used by P$1$ : while$($S$1==$S$2)$; Critical section S$1=$ S$2$; Method used by P$2$ : while$($S$1!=$S$2)$; Critical section S$2=$ not$($S$1)$; Which of the following statements describes properties achieved? Select one: a$.$ Neither mutual exclusion nor progress b$.$ Mutual exclusion but not progress c$.$ Both mutual exclusion and progress d$.$ Progress but not mutual exclusion