Answer :

AL2006
From the list of choices that you have provided,  √x + 2  is the greatest value.

I honestly don't see what  2 < x < 6 has to do with anything.
well
2≤x≤6
so the values of x are: 2,3,4,5,6
and if we replace the values of the answers 
if we replace x by 2 A√2=1.4 ;B √2+1=√3=1.7 ;C √2-1=√1=1 ;D√2-2=0 
if we replace x by 3 A√3= 1.7     ;B √3+1=√4= 2   ; C √3-1=√2=1.4 ;D √3-2=√1=1
if we replace x by 4 A √4= 2   ;B √4+1=√5=2.2  : C √4-1=√3=1.7; D√4-2=√2=1.4
if we replace x by 5 A √5= 2.2 ;B √5+1=√6=2.44;C √5-1=√4= 2   ;D√5-2=√3=1.7
if we replace x by 6 A √6= 2.44;B √6+1=√7=2.65;C √6-1=√5= 2.2  ;D√6-2=√4=2

you will notice that the group of answers B has the greatest values so the answer is :B