Final answer:
The box's rate of acceleration when released by Sean in the warehouse is 9.8 m/s^2, as this is the acceleration due to Earth's gravity.
Step-by-step explanation:
When Sean releases the box in the warehouse, the box's rate of acceleration is solely due to the force of gravity, as there are no other forces acting on it (assuming air resistance is negligible). The standard acceleration due to gravity on Earth is 9.8 m/s2. Thus, the correct answer to what the box's rate of acceleration will be when Sean releases it is a) 9.8 m/s2, which is also acknowledged by other references to objects dropping under the influence of gravity.