Choose the correct statements about the principles of ecology.
\[
\begin{aligned}
A.&\ \text{Ecosystem is a fundamental unit of ecological study.}
B.&\ \text{Physical and biological processes do not follow the principles of uniformitarianism.}
C.&\ \text{All living organisms and physical environment are mutually reactive.}
D.&\ \text{Ecosystem functions through the input of energy, mainly solar.}
\end{aligned}
\]
Choose the correct answer from the options given below: