—‘Look, sheriff,'said Rockwall,‘don't be too hard on us. I'm Rockwall Slinger and this is Merlin Greeves.'

—‘Oh, is it?' said the sheriff with a sneer.

【翻译】

—“瞧，警长，”罗克沃尔说，“不要太为难我们了。我是罗克沃尔.斯林格，这是默林.格里夫斯。”

——“哦，是吗？”警长冷笑着说。

【分析】Is it?  是吗？是吧？

Is it? ——这叫做 SENTENCE SUBSTITUTE （句子的代用语）： an expression used in response to a statement, sometimes to seek conformation, but often merely to show that one is listening.

这是一个对某一陈述作出反应的表达，有时是为了得以确认，通常只表示说此话者正在倾听。