A unique code is assigned to all test takers of the GNAT exam on a specific day in a center. On 12 Jan 2021, there were 32 test takers with the codes. The codes are either 2-letter codes or 3-letter codes in alphabetical order. How many letters will the center need at a minimum to give all the test takers a unique code?
A. 5
B. 6
C. 7
D. 8
E. 9
Answer: B
Source: e-GMAT