Answer:
Your answer would be B.
Step-by-step explanation:
Your answer would be because the sentence contains a string of coordinate adjectives. Coordinate adjectives are adjectives in a row that each separately modify the noun they precede. In this case, both "cold" and "sunny" modify "days". It's also possible to rearrange the adjectives. That's why said adjectives should be separated with a comma.
On the contrary, cumulative adjectives are also placed next to each other before the noun they modify. However, the adjective right before the noun pairs up with the noun as a unit, and the adjective before the unit modifies that. They do not separately modify the noun, so a comma should not separate this type of adjectives.