您好，这两句话个人的理解是：
1）The districts most
affected were Ratnapura, 100km southeast of Colombo and Kalutara, about
40km south of the capital, which both had a series of landslide
after the terrible rain.
这一句话比较难的在于这两个逗号，因为两个逗号可以算是非限定性定语从句的标配，表示逗号之间的句子是可以省略的，那么句子就变成了 The districts most
affected were Ratnapura, about
40km south of the capital, which both had a series of landslide
after the terrible rain. 假如省略了，那么就意味着 Ratnapura 距离 Colombo 和 Kalutara 的距离都是东南面的100公里，而 Ratnapura 距离首都是南面的 100公里。
这样分析显然是不对的，因为 Sri Lanka 的首都就是 Colombo，而 Colombo 对于 Ratnapura 来说，不可能同时间是东南面 100 公里，和南面 40公里了。所以的两个逗号就不是省略的非限定性定语从句，而是由 and 并列的句子了。所以句子就是：
The districts most
affected were Ratnapura and Kalutara, which both had a series of landslide
after the terrible rain.
所以（100 km southeast of Colombo) 是后置定语修饰 Ratnapura，而（about 40km south of the capital）是后置定语修饰 Kalutara；受灾害的是 Ratnapura 和 Kalutara 这两个城市，Colombo 就是 Capital，所以 Ratnapura 位于 Colombo 东南面的100公里，而 Kalutara 位于 Colombo 南面的40公里，也就可以总结出受灾害的是 Colombo（Capital）南面的两座城市 Ratnapura 和 Kalutara 了。
2）Sri Lankan President XXX
was scheduled to return to Colombo Friday night after a two-day state
visit to Australia and planned to hold an emergency meeting with
emergency officials to discuss relief operations.
这一句的主干也是个由 and 连接的并列句：
Sri Lankan President XXX
was scheduled to return to Colombo Friday night and planned to hold an emergency meeting.
也就是 somebody was scheduled to return to somewhere and planned to do somethnig. 这里的 was scheduled 和 planned 并列了。
所以 after a two-day visit to Australia 是（after 引导的介词短语充当句子的时间状语）修饰 was scheduled to return，而 after 这个介词表示连接的动作先发生，主句的动作后发生。所以（访问澳大利亚）完了之后再回到 Colombo，与此同时，planned to hold（打算举办一个紧急会议），所以（访问澳大利亚）在（举办紧急会议）之前，因为人没有回来，就无法和 emergency officials（紧急情况官员）discuss relief operations（探讨缓解工作），而 after 的时间状语和 was scheduled 是一起的。
希望这样的分析可以帮助到您。

第一个有两种方法判断。

第一种常识判断法。如果常识知识比较丰富的话可以知道about 40km south of the capital不可能指代的是前面的Colombo and Kalutara，因为Colombo就是capital。

第二种方法是”一句话只能有一个主语"的法则。首先我们确定句子描述的主语是谁，是 Ratnapura，那么这句话后面不带主语的都是在描述Ratnapura。

第二个，通过时态判断还有长句化短句。前面有答主提到了，没错就是and，找到and非常关键，因为and意味着连接的两部分是并列关系。

Sri Lankan President XXX was scheduled to return to Colombo Friday night | after a two-day state visit to Australia| and planned to hold an emergency meeting with emergency officials to discuss relief operations.

可以看到加粗的部分就是and连接的两个动词，时态也是一样的，把after a two-day state visit to Australia删掉看看不能不能理解。

scheduled to return to Colombo Friday night and planned to hold an emergency meeting with emergency officials to discuss relief operations.

这样是不是很清楚的知道，周五晚上回科伦坡，并且，举行紧急会议。

可以知道紧急会议就是在周五晚上，地点就是在科伦坡。

加上 | after a two-day state visit to Australia| 再看看，可以知道周五晚上回科伦坡是在对澳大利亚两天国事访问之后。

所以可以知道，在澳大利亚访问后，总统计划周五回到科伦坡并且举行紧急会议。

“首都南部约40km”描述的是Kalutara，遭遇滑坡的是Ratnapura和Kalutara。这段话的意思是“受灾最严重的地区是位于Colombo东南100公里的Ratnapura和首都以南约40公里的Kalutara，这两个地区在这场可怕的降雨后都发生了一系列滑坡。” 句子中的and连接两个并列的成分。

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