长难句与篇章结构

① 报数写法：作者说 two key factors，本段只写了一个——另一个在下一段。读到报数句就预判段落结构：并列还是递进。

段 A Two key factors led to the decline of the tram system. The first was cost: running buses on ordinary roads was much cheaper than keeping the rails in repair.

段 B The second factor was speed. As city roads grew busier, trams that shared those roads became slower and slower.

② 三段并列 + 内容递进：多段并列展开同一主题时，后段常在前段的基础上加深。

③ 读不读（与 R5 信号词表同源）：举例、解释之后不必读；总结、因果之后必要读；并列、递进之后看前一句是概括还是细节——概括就读，细节就不用读。