上过这门课的同学都应该知道，我们一般会通过观察砂岩中的颗粒类型，也就是砂岩中的实际颗粒，来确定它的来源。

As everyone in this class should know, we usually look at the grain type within sandstone, meaning the actual particles in the sandstone, to determine where it came from.

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下面所列的几种听者常常让谈话难以进行，观察别人，我们很容易发现这些类型。

Here, in brief, are a few types of listeners that make conversation difficult. Its easy to see others in these roles.

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接下来，观察模式引进的新复合类型。

Next, look at the new complex types introduced by the schema.

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