A sole proprietor has applied for and acts under a DBA. Under federal law, the tax return that must be filed is a(n)

individual return form 1040 with schedule C attached. (DBA is doing business as. Sole proprietor)

Explanation:

Since in the question it is mentioned that A sole proprietor is applied for and acts that covered a doing business as DBA

So according to the federal law , the tax return that should be filed as an individual return under the form no 1040 that comes under the schedule C which is attached.  

The same is to be considered

answer(b); ; ; the quantitative or qualitative variable for which the experimenter wishes to determine how its value is affected by the explanatory variable;