This word means the same as the given italicized word. Hence option C is correct.
Option A: 'Indefinite' means 'lasting for an unknown or unstated length of time'.
Option B: 'Imminent' means 'about to happen'.
Option D: 'Improbable' means 'not likely to be true or to happen'.
These words do not mean the same as the given word 'inevitable'.
So, options A, B and D are wrong.