column names are case-sensitive. Fix: `df["country"]`. 2. **ValueError** — use `&` instead of `and`, and wrap conditions in parentheses. Fix: `df[(df["coverage_pct"] > 90) & (df["year"] == 2022)]`. 3. **KeyError** — multiple columns need double brackets. Fix: `df[["country", "region"]]`. 4. **Settin