Concept:An antonym is a word opposite in meaning.
Unfavourable weather is bad, harsh weather that causes problems (here, it affected their health).
Solution:The opposite of unfavourable (bad, harmful) weather is good, agreeable weather, that is,
pleasant weather.
"Beautiful" describes how something looks, not whether weather is good or bad for people.
"Cool" only describes temperature; cool weather can itself be unfavourable.
"Promising" means showing signs of future success; it is not the opposite of
unfavourable when describing weather.
Key point: The stored key gave (C) cool, which is not an opposite of
unfavourable. The opposite is
pleasant (favourable).
Answer:Option B (pleasant)