oh..
first, lets assume the there are five numbers
a1,a2,a3,a4,a5. with a reminder 0,1,2,3,4. these are the only five reminders that FIVE could have.
thus, when a1+2,a2+2......a5+2. divide by 5. the reminder will become 2,3,4,0,1. So, the reminder is also unique.
and for2*a1, 2*a2,..., 2*a5,
it will be 0,2,4,1,3. which is also unique.
and for a1^2, a2^2,..., a5^2.
it will be 1,4,4,1,0. which is not unique.
so, the answer is A and B. | 
