If a, b, c, and d are positive numbers, is ab<cd? 0<c−ad−b (adbc)2<adbc

If a, b, c, and d are positive numbers, is

\frac{a}{b} < \frac{c}{d}

A、Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B、Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C、BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D、EACH statement ALONE is sufficient.
E、Statements (1) and (2) TOGETHER are not sufficient.

答案：B

问题：老师这里的B怎么推断呢 2）我只能判断出它是abcd小于1 其他有点看不出来了。然后可以也同时问下图中的27题该如何解答呢答案是不是C呢谢谢老师查看答疑

问题：请问这种不等式的题目怎么解答啊？感觉就是不等式变化比较多，很难掌握。像我在判断1单独sufficient还是不sufficient的时候也觉得要代数字进去然后浪费不少时间。我看了网上解释条件2的部分也不是很明白。望老师可以指点一下，我没有在国内上过高中。不等式对我来说是个难点。谢谢！