▲书上的解释是对的。last 其中有个用法就是表示“最不可能的”“最不合适的”，其后通常接不定式作定语或接定语从句。又如： 

The last thing I want to do is to offend you. 我最不想使你生气。 

She’s the last person to trust with a secret. 她是最不可能保密的人。

Mary is the last person you’d see in a pub—she hates pubs. 玛丽最不可能去酒吧——她讨厌酒吧。

He never crossed my path, thank goodness. He was the last person I wanted to meet. 谢天谢地，我们从来没碰上过。我最不愿意见到的就是他。

▲要注意以上用法与 last 表示“最后一个”时的区别（主要应根据句意来区分）。如：

He was the last to take the floor. 他最后发言。

He was the last to arrive. 他是最后一个到的。

Steve, as usual, was the last to arrive. 史蒂夫照例来得最晚。

I was the last to leave the warehouse, so I locked up. 我最后离开仓库，因此锁上了门。

The porter was the last person to see her prior to her disappearance. 那个搬运工是在她失踪前见过她的最后一个人。

She’s as keen as mustard. She always gets here first in the morning and she’s the last to leave work in the evening. 她工作极其热情，总是最早来，最晚走。

▲如果没有特定的上下文，有时可能有歧义。如：

He is the last person to be asked to speak. 

理解一：他是最后一个被邀请发言的人。

理解二：最不该邀请他来发言。