你以为 untouched 是由untouch变化的过去分词，然后才转化成的形容词。其实，untouched 是这样构成的：touch → touched → untouched。其实类似的构词情况很多：

The question was unexpected. 那种质问完全是出乎意料的。

The match was left undecided. 比赛没有分出胜负。

The land reform question remained unsolved. 土改的问题仍没解决。

To my surprise the door was unlocked. 使我吃惊的是门没锁。

He emerged from the accident unharmed. 他在车祸中没有受伤。

Being unemployed, he hasn’t got much money. 由于他没有工作，他没有多少钱。

Her colleagues had deliberately kept her uninformed. 她那些同事故意不让她知道。

I discovered [found] an unopened letter in the drawer. 我在抽屉里发现有一封未启开的信。

He often came to watch the boats being loaded and unloaded. 他常常到这里来看轮船装货卸货。

I wouldn’t have the cheek to go to the party uninvited. 不邀请我是不会厚着脸皮去参加晚会的。

I have two brothers—one is married and the other is unmarried. 我有两个兄弟，一个结了婚，一个还是单身。