To succeed in the modern world, one needs several key qualities discipline, creativity, and resilience.
Correct: C
Option C correctly uses a colon to introduce a list that elaborates on or explains the preceding independent clause. The phrase 'several key qualities' sets up the expectation for a list of those qualities. Options A and B use a semicolon or an em dash, respectively, which could be used in similar contexts but the colon is the most precise and standard choice here for introducing a direct list. Option D creates a comma splice and fails to properly introduce the list.