1. Suppose there are two propositions:
   Proposition A: $a$ is a real number greater than zero; Proposition B: $a > b$ and $a^{-1} > b^{-1}$, then
   (A) A is a sufficient but not necessary condition for B
   (B) A is a necessary but not sufficient condition for B
   (C) A is a sufficient and necessary condition for B
   (D) A is neither a sufficient condition nor a necessary condition for B
(B)
I. Multiple Choice Question
1. 【Analysis and Solution】Since "Jia" being true does not necessarily mean "Yi" is true (for example, when $a=3, b=2$, "Jia" is true, but "Yi" is not true), it can be concluded that "Jia" is not a sufficient condition for "Yi".
Next, let's consider under what conditions "Yi" is true. Clearly, "Yi" is true if and only if $a>0$ and $b<0$. Therefore, it can be concluded that "Jia" is a necessary condition for "Yi". In summary, "Jia" is a necessary but not sufficient condition for "Yi".