Which sentence tells why zejd coralic had a problem at school?

a) in september 2015, zejd was 6.
b) zejd coralic is a young boy who lives in sarajevo.
c) he started first grade.
d) he was not able to communicate with others.

The correct answer is:  [D]:
 
         "He was not able to communicate with others."

Note:  

Choice [A]:  "In September 2015, Zejd was 6."  
   This was not Zeid problem in school; so this choice is incorrect.

Choice [B]:  "Zejd Coralic is a young boy who lives in Sarajevo."
    Again, this was not Zejd's problem in school; so this choice is incorrect.

Choice [C]:  "He started first grade."
    Again, this was not Zejd's problem in schoo; as such, this choice is incorrect.

We are left with:

Choice [D]:  "He was not able to communicate with others."
    This was Zejd's initial problem in school;  as such, this is the correct choice.