Which of these statements is true regarding the preamble to the constitution of the united states?
a. it establishes the three branches of government.
b. it defines the role of the states to the federal government.
c. it sets up the power of the states over the people.
d. it explains the purposes of the constitution.

The answer is letter d. It explains the purposes of the Constitution.
The Preamble to the U.S. Constitution is a brief introductory statement of the basic or  fundamental purposes and guiding principles of the constitution. It says in general terms, and referred by the courts to it as reliable evidence of, the intentions of the Founding Father regarding the Constitution's meaning and what they hoped the Constitution would achieve. 

Possess private property.