1. The problem is to identify the financial concept where compounding and payment periods happen simultaneously. 2. Let's define the terms: - Simple annuity: Payments are made at regular intervals, but interest is not compounded within the payment period. - General annuity: Payments and compounding periods may differ. - Compound interest: Interest is calculated on the initial principal and also on the accumulated interest from previous periods. - Simple interest: Interest is calculated only on the principal amount. 3. When compounding and payment periods coincide, the annuity is called a simple annuity. 4. Therefore, the correct answer is **Simple annuity**.