She is allergic _____ peanuts.

**The reasoning** In English, certain adjectives pair with specific prepositions — we call these **fixed collocations**. "Allergic" always takes the preposition **"to"**. This isn't about logic; it's simply how the language has evolved. Just like we say "afraid of" (not "afraid from") or "interested in" (not "interested with"), we must say "allergic to." So: "She is allergic **to** peanuts" is the only correct form. **Why the wrong options tempt you** - **"from"** might seem logical because you think of the allergy coming *from* peanuts, but that's not how we express this relationship in English. - **"with"** feels like it could work because you might think she has a problem *with* peanuts, but again, "allergic" doesn't pair with "with." - **"of"** is close to other common phrases like "afraid of," so your brain might automatically reach for it — but it's the wrong partner for "allergic." **Quick takeaway** Memorize this: **"allergic to"** is a fixed phrase — the preposition never changes, no matter what follows.