QUESTION $21C(n,r)=$ a$.\frac{n!}{(n-r)!}$ where $1rn$ b$.\frac{n!}{r!(n-r)!}$ where $1rn$ c$.\frac{r!n!}{(n-r)!}$ where $1rn$ d$.r!n!$ where $1rn$ QUESTION $21C(n,r)=$ a$.\frac{n!}{(n-r)!}$ where $1rn$ b$.\frac{n!}{r!(n-r)!}$ where $1rn$ c$.\frac{r!n!}{(n-r)!}$ where