array of array

[target___]

hello, im a student and im new at programming ( c ), i want learn c for using microprocessor programming, i dont find the answer of this problem, if you know, please help me. i want to create an array of array similar this;
for example i have got three constant array

unsigned char a_0[]={0x54,0x25,0x11,0xff,0x21};
unsigned char a_1[]={0x51,0x45,0x55,0x85};
unsigned char a_2[]={0x24,0x47};

in program i want to use those costants similar this;
send(a[0]);

or i=2;

send(a[i]);

how can i do this, all my constants have got different size

[Salem]

unsigned char *arrs[ ] = {
  a_0,
  a_1,
  a_2,
};

send( arrs[i] );

[target___]

thank you