\textbf{71.} According to the figure, three immiscible liquids are poured into a tube. Which relationship between the pressures at the marked points is correct?
\begin{center}
\textit{[Figure: A U-shaped tube with three immiscible liquids; points A, B, C, D are marked at various levels in the tube.]}
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\begin{enumerate}
\item[(1)] $P_A > P_B > P_C = P_D$
\item[(2)] $P_A = P_B > P_C > P_D$
\item[(3)] $P_A - P_C = P_B - P_D$
\item[(4)] $P_A + P_C = P_B + P_D$
\end{enumerate}