You know that when you take the average of two numbers you
divide by 2. So multiply each choice by 2 and see if they could be
the sum of any 2 numbers from the list:
1 3 4 5 11
I. 3 3*2=6 (5+1=6—yes)
II. 4 4*2=8 (3+5=8—yes)
III. 6 6*2=12 (11+1=12—yes)
So I, II, and III all could be the average, so E is correct.