Which of the following sum is in the simplest form?

• A.  \[\frac{4}{9}+\frac{-5}{9}\]                       
• B.  \[\frac{-2}{5}+\frac{13}{20}\]       
• C.         \[\frac{-5}{12}+\frac{11}{-12}\]    
• D.         \[\frac{-7}{8}+\frac{1}{12}+\frac{2}{3}\]