Final answer:
The word 'malevolent' refers to having or showing a wish to do evil to others, which means its closest definition is (b) Evil.
Step-by-step explanation:
The underlined word 'malevolent' in the sentence 'The people believed that malevolent forces were at work' most nearly defines an intent or nature that is evil. The term 'malevolent' is rooted in Latin, with 'male' meaning 'bad' or 'evil' and 'volent' from 'volens' meaning 'wishing or wanting'. Together, they form a word that describes a desire to do evil or harm to others. It is distinct from 'good', which implies beneficial or positive intentions, 'supernatural', which relates to phenomena beyond the natural world without a value judgment of good or evil, and 'fortunate', which implies luck or good fortune. Therefore, the correct answer to the question is (b) Evil.