Weber Corporation was incorporated in the State of Delaware. It does all of its business in several adjoining states. Under the circumstances?

a. Weber's Delaware corporation was invalid because it does no business there.

b. Weber is a domestic corporation in all states based upon full faith and credit.

c. Weber will not have to pay corporate income taxes except to Delaware and the United States.

d. Weber should either incorporate in the adjoining states where it does business or otherwise qualify to do business therein.

Under the circumstances described in the question which answer applies?