Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
I believe both A and D are correct, but A is less wordy. Therefore, A.
Note: In fact, I've realized this is not the 1st time the GMAT throws more than 1 feasible answer choice, and leaves us the task to determine which one is more appropriate (as opposed to just throwing plain wrong choices).