Meaning of the Derivative in Context Practice Test

At $t=0.5$ hours, hours increase at 90 hours per ppm.

At $t=0.5$ hours, CO$_2$ level is 90 ppm.

At $t=0.5$ hours, CO$_2$ increases at 90 ppm per minute.

At $t=0.5$ hours, CO$_2$ level is increasing at 90 ppm per hour.

In the first 0.5 hours, CO$_2$ increased by 90 ppm total.