Which of the following statements is true?
a. economists almost always find it easy to conduct experiments in order to test their theories.
b. economics is a social science rather than a true science because it cannot employ the scientific method.
c. economists are usually not allowed to conduct experiments, and so they must rely on natural experiments offered by history.
d. economics is not a true science because economists are not usually allowed to conduct experiments to test their theories.

The answer is: C)Economists are usually not allowed to conduct experiments, and so they must rely on natural experiments offered by history. This is only partially true. Option B could also be considered a possibility but the term "True Science" is not properly used. In order to consider that answer the term would need to be changed to "Natural Science".

Explanation:

Economics is a social science like law and anthropology,. It is divided into 2 different fields: Macroeconomics and Microeconomics. They rely heavily on interpretation and qualitative research methodologies, but also use statistics and mathematical theories to test hypotheses and forecast trends.  On the other hand, natural sciences like physics rely on the scientific method to test their hypotheses.

Macroeconomics deals with the economy of a whole country or region. Since their are too many variables involved in an economy, it is impossible to conduct a Macroeconomic experiment. Testable hypotheses don´t exist in Macroeconomics. No one can guarantee if and how plan A or plan B will make the American economy grow at a 3% yearly rate.  

But the scientific method can be applied in Microeconomics (studies the actions of an individual unit). It is possible to conduct quantitative studies that produce verifiable and retested results.