背景： 这篇课文以日本城堡的防御策略为主题，与学生对历史和工程的兴趣相符。

核心语言重点： 被动语态。

课文：

Japanese castles were not only beautiful buildings but also powerful fortresses. They were built to protect a lord and his people from attacks. The main part of the castle, called the keep, was always placed on the highest ground. The entire castle was surrounded by thick walls and a deep moat. Sometimes, traps were placed at the main gate. The castle walls were often built with huge, carefully shaped stones that were not held together by mortar. This design was chosen so that the walls would be more resistant to earthquakes. The most important parts of the castle were always protected by the strongest defenses. Many secrets are hidden inside the walls, and these are still being discovered by historians today.

词汇亮点：

fortresses 要塞

keep 主楼

moat 护城河

mortar 砂浆

historians 历史学家

语法解析：

这篇课文是练习被动语态的绝佳范例，特别是在描述历史事件时，当执行动作的人并不重要或未知时，被动语态尤为有用。课文中的例子包括“Japanese castles were not only beautiful buildings but also powerful fortresses”和“The castle walls were often built with huge, carefully shaped stones”。在这些句子中，被动语态强调了动作本身（被建造、被放置），而不是执行动作的人。这为学生提供了一个在技术性或历史性写作中如何使用被动语态的清晰模型。