What is the difference in the rights granted by a common-law trademark and a federally registered trademark?

Select one:

a. A federal registration constitutes nationwide constructive use, whereas a use that gives rise to a common-law trademark creates rights only around the geographic area of use.

b. A federally registered trademark can become incontestable after five years of registration.

c. Use is not required to obtain or maintain a federally registered trademark.

d. Both A and B