$6.$ Consider the following function definition: void tripler$($int n$)\{$ n $=3*$n; $\}$ Given this definition, which of the following are acceptable function calls? Why? $(2$points$)$ int a$[3]=\{3,4,5\},$ number $=2$; a$)$ tripler$($a$[2])$; b$)$ tripler$($a$[3])$; c$)$ tripler$($a$)$; d$)$ tripler$($number$)$;