Step 1: Understand primary vs secondary affixes.
Primary affixes attach directly to root/base forms, while secondary affixes attach to already affixed forms.
Step 2: Analyze *grammarismian.
The affix {-ism} typically forms abstract nouns from bases (e.g., {grammar} → {grammarism}). The affix {-ian} is a primary affix and must attach directly to the base. However, in {grammarismian}, {-ian} is trying to attach to a derived word ({grammarism}), which is not allowed for a primary affix.
Thus, the ungrammaticality arises due to:
(A): {-ian} being a primary affix (shouldn't attach to a derived base),
(D): {-ism} being a secondary affix implies it's already derived, leading to an ill-formed base for {-ian}.