1. **Problem statement:** Find an explicit formula for the sequence defined by $a_1 = -4$ and the recursive relation $a_n = a_{n-1} + 9$ for $n \geq 2$. 2. **Understanding the problem:** This is an arithmetic sequence where each term increases by a constant difference of 9. 3. **Formula for arithmetic sequences:** The explicit formula for the $n$-th term of an arithmetic sequence is: $$a_n = a_1 + (n-1)d$$ where $a_1$ is the first term and $d$ is the common difference. 4. **Identify values:** Here, $a_1 = -4$ and $d = 9$. 5. **Substitute values into the formula:** $$a_n = -4 + (n-1) \times 9$$ 6. **Simplify:** $$a_n = -4 + 9n - 9 = 9n - 13$$ 7. **Final explicit formula:** $$\boxed{a_n = 9n - 13}$$ This matches option A.