One who cannot easily pleased:

A. Cosmopolitan

B. Frightening

C. Fastidious

D. Feminist

Answer: Option C

Solution(By Examveda Team)

The one word substitution is Fastidious.

Cosmopolitan : familiar with and at ease in many different countries and cultures.
Frightening : making someone afraid or anxious; terrifying.
Feminist : a person who supports feminism.
Fastidious : very attentive to and concerned about accuracy and detail.