Build a short mental table of what each of the four terms is used for, then match it against the question.
Bond's index, energy needed to grind material, units of kilowatt-hour per ton, tells you how hard the machine has to work, not how uniform the output is.
Work index, this is simply another name for the same energy constant used in Bond's law of size reduction. Same category as Bond's index, again about energy, not uniformity.
Fineness modulus, calculated purely from a sieve analysis of the ground sample itself, by definition it is described in process engineering references as the index of the uniformity of grind in the resultant product.
"Uniformity index", not a standard defined term for this purpose in the relevant syllabus, it is included only as a plausible-sounding distractor.
Matching the question's exact phrase, "uniformity of grind", to the term that is actually defined that way leaves only one candidate.
\[\boxed{\text{(A) Fineness modulus only}}\]