A list of 8 student test scores is to be sorted into ascending order using a merge sort algorithm.
Figure 1 shows a partially completed tree diagram representing this sorting process.
a.[2]
State the contents of the blank boxes labeled A, B, C, and D.
b.[2]
Explain how the merge sort algorithm operates, with reference to the "divide" (rows 1–4) and "merge" (rows 4–7) phases of the process shown in Figure 1.