Consider the following code fragment.struct Date$\{$int month;int day;int year;struct Student$\{$string name;double gpa;Date d$1$;$\}$;Student S$1$;Date d$2$;Which of the following statement will cause a compilation error?O $($a$)$ S$1\mathrm{.}2.$year$=1972$; b$)$ S$1.$d$1=1972$;O c$)$ d$2.$year$=1972$; d$)$ Both $($a$)$ and $($b$)$