Consider the following file from some larger C program:

int a;
extern int b;
static int c;
void foo() {
    int a;
    static int b;
    extern int c;
    extern int d;
}
static int b;
extern int c;
For each variable declaration, indicate whether the variable has external linkage, internal (file-level) linkage, or no linkage (i.e., is local).