Final answer:
The acid with an acid dissociation constant of 4.7×10-3 is the stronger acid.
Step-by-step explanation:
An acid dissociation constant, also known as Ka, is a measure of the strength of an acid. The larger the value of Ka, the stronger the acid. In this case, we are comparing two acids with different Ka values.
Option B has an acid dissociation constant of 4.7×10-3, which is larger than the acid dissociation constant of 3.9×10-4 for option A. Therefore, option B is the stronger acid.