Question

folly (noun)
1 very carefully and delicately
2 fearful or uneasy anticipation; dread
3 an act or instance of foolishness
4 feeling or showing little emotion

Explanation:

To solve this, we analyze the meaning of "folly" (noun). "Folly" means a foolish act or idea. Option 1 describes a careful manner, Option 2 is about dread, Option 4 is about being unemotional. Option 3 ("an act or instance of foolishness") matches the definition of "folly".

Answer:

1. an act or instance of foolishness