Question 461933
c) 9.

Since the terms of the sum are all positive integers, then the least value any of the terms can take is 1.  The second least positive integral value one of the remaining terms can take is 2.  (Remember the value of the next term is distinct from the first, and hence higher.)  The value of the remaining term must then be maximal, which is 12 - 1 - 2 = 9.