Answer: Both linear trend models and log-linear trend models

## Explanation Both linear trend models and log-linear trend models are regression models with a single independent variable: - **Linear trend models**: Use time as the independent variable (e.g., y_t = b_0 + b_1t + ε_t) - **Log-linear trend models**: Also use time as the independent variable but with a logarithmic transformation (e.g., ln(y_t) = b_0 + b_1t + ε_t) Both models have time as their single independent variable, making option C the correct answer.

Author: LeetQuiz Editorial Team