Thrust is a force. The SI unit of force is Newton (N), which is equivalent to $\text{kg} \cdot \text{m/s}^2$. Impulse is the change in momentum, or force multiplied by time. The SI unit of impulse is N·s, which is equivalent to $(\text{kg} \cdot \text{m/s}^2) \cdot \text{s} = \text{kg} \cdot \text{m/s}$. The ratio $\frac{\text{Thrust}} {\text{Impulse}}$ has units $\frac{\text{N}} {\text{N} \cdot \text{s}} = \frac{1}{\text{s}}$. The unit $1/\text{s}$ is the unit of frequency. Frequency is the number of cycles or events per unit time, measured in Hertz (Hz), where 1 Hz = $1/\text{s}$. Let's check the units of the options: A) Frequency: $1/\text{s}$ or Hz. B) Speed: m/s. C) Wavelength: m. D) Acceleration: m/s². The unit of the ratio is the same as the unit of frequency.