Here are the spaces:
___ ___ ___ ___ ___ ___
1 2 3 4 5 6
>>...person D stands in space six with no one beside him...<<
So we have this, with 0 indicating the empty space
___ ___ ___ ___ _0_ _D_
1 2 3 4 5 6
So all the other spaces 1 through 4 are filled.
>>...Person E is the third person from the left...<<
So we have
___ ___ _E_ ___ _0_ _D_
1 2 3 4 5 6
>>...Person A is to person B's immediate left...<<
The only two adjacent spaces remaining are spaces 1 and 2,
so we have
_A_ _B_ _E_ ___ _0_ _D_
1 2 3 4 5 6
>>...where is person C?...<<
C is in the only remaining space, 4:
_A_ _B_ _E_ _C_ _0_ _D_
1 2 3 4 5 6
Edwin