Example 1. Let $\mathrm{A}$ be a sufficient condition for $\mathrm{B}$, $\mathrm{B}$ be a sufficient condition for $\mathrm{C}$, $\mathrm{C}$ be a necessary and sufficient condition for $\mathrm{D}$, $\mathrm{E}$ be a necessary and sufficient condition for $\mathrm{D}$, $\mathrm{F}$ be a necessary condition for $\mathrm{D}$, $\mathrm{F}$ be a sufficient condition for $\mathrm{G}$. What kind of condition is $\mathrm{A}$ for $\mathrm{G}$? What kind of condition is $\mathrm{G}$ for $\mathrm{E}$?
From the given information, we have
$$
\begin{array}{l} 
A \Rightarrow B \Rightarrow C \Longleftrightarrow D \Leftrightarrow E \\
\downarrow \\
F \Rightarrow G
\end{array}
$$

According to the symmetry and transitivity of necessary and sufficient conditions, and the transitivity of sufficient and necessary conditions, we can conclude that $A$ is a sufficient condition for $G$, and $G$ is a necessary condition for $E$.