Concept: Natural law theory is based on reason, morality, justice and universal principles. It believes that law should reflect rational and moral standards.
Step 1: Understand natural law.
Natural law is not based merely on commands of the sovereign. It is based on higher principles of justice, morality and reason.
\[
\text{Natural Law} = \text{Reason + Morality + Justice}
\]
Step 2: Understand the role of reason.
Natural law thinkers believe that human reason can discover basic principles of right and wrong.
\[
\text{Reason} \Rightarrow \text{Universal principles of law}
\]
Step 3: Select the correct basis.
Among the given options, the most suitable basis of natural law is rational and reasonable needs of mankind.
Therefore, the correct answer is option (A).