Multidimensional Length

Hi, im sure this is really simple but for some reason I have not found any helpful info on this. I am trying to get the length of arrays within an array, here is my example (MX 2004):

this.menu.o= [“option1”,"",“container”],[“option2”,"",“container”];
context=“o”;

trace(this.menu[context].length);

I get an output of of 3. the number of variables within the first array, this is not what I had expedted. Any help in pointing out my error would be much appreciated.