Simple distillation needs boiling points more than about 25 K apart.

Step 1. (a) $351\ \text{K} - 338\ \text{K} = 13\ \text{K}$: less than $25\ \text{K}$, so fractional distillation.

Step 2. (b) $384\ \text{K} - 329\ \text{K} = 55\ \text{K}$: more than $25\ \text{K}$, so simple distillation.

Step 3. (c) $391\ \text{K} - 373\ \text{K} = 18\ \text{K}$: less than $25\ \text{K}$, so fractional distillation.