Let $D$ be one domain and $M$ and $N$ are different maximal ideals. Show that $M + N = D$.

Question

Since $ M $ is maximal then $ M \subsetneq D $ the same is for $ N $, so there is no $ J $, such that $M \subsetneq J \subset D$ and $N \subsetneq J \subset D$. Given this, can I conclude that $M + N = D$?.