The letter pattern a a _ b a _ b _ _ a b _ is made by repeating one block. Which letters fill the blanks from left to right?

Explanation

1. 01

   The pattern has 12 places. Try blocks of 4: aa_b | a_b_ | _ab_.

2. 02

   The block aabb fits all the letters that are shown.

3. 03

   Filling each block as aabb gives the blanks b, a, b, a, b, and the pattern aabbaabbaabb.