Explanation:

The original sentence is erroneous.

Reason: The correct idiomatic expression is 'keep his chin up' and not keep his cheek upwards'.

Keep one’s chin up (Idiom):

Meaning: To stay cheerful and hopeful during difficult times.

E.g.: Keep your chin up, we're not lost yet.

 Hence ‘keep his chin up’ should be used in place of ‘keep his cheek upwards’ to make the sentence grammatically correct.

Among the given choices, only option C replaces the given bold part most appropriately.

The sentence after replacement becomes:

It is essential for an entrepreneur to keep his chin up despite failures and setbacks.

Option C is hence the correct answer.