looking for an array-extract-item-as-it operator

I need to access an array-item from an array of arrays. Suppose

WITH t AS (SELECT '{{1,2,3},{33,44,55}}'::int[][] as a)SELECT
a[2], -- returns null (!), why not works?
a[2:2], -- returns array-into-array, not a simple arrayFROM t;

There are a simple function or operator to acess it as it?

Summarizing: I am looking for a f(a,2) that returns {33,44,55}, not
{{33,44,55}}.