1. But there was really only one way to get her throne back, an appeal to her cousin Elizabeth.

結構分析：這個句子是個簡單句，其中的to get her throne back是動詞不定式做定語修飾名詞way。

An appeal to her cousin Elizabeth是名詞性短語作同位語，做way的同位語，說明這個方式是什么。

2. She must have supposed her stay would last a month, a year at the most.

結構剖析：這是含有賓語從句的復合句。主句是：She must have supposed，從句是：her stay would last a month, a year at the most。

主句使用了虛擬語氣。主句的謂語結構是：must have supposed。這個屬于情態動詞的虛擬語氣的用法，must have done表示對過去了的事情非?？隙ǖ牟聹y。

3. Had she known the real answer,19 years, she would surely have avoided the passage across the Solway Firth.

結構剖析：這句話是非真實條件虛擬句。主句是she would surely have avoided the passage across the Solway Firth，條件狀語從句是：Had she known the real answer, 19 years。

條件狀語從句中由于省略了if這個引導詞，就必須采用倒裝句式，將助動詞had提到句首：had she known the real answer。

這個復合句使用了虛擬語氣，主語的謂語結構是would have avoided，提煉一下就是would have done這個結構，表示與過去事實相反的情況。（詳細分析：瑪麗女王不知道橫渡Solway海灣到達大不列顛需要19年，如果知道的話，她就不會采用這條路線走，可是事實瑪麗女王采用的是這條路線。）

由于主句采用的是過去時態would，那么要注意從句和主句的時態相呼應，由于know the answer這個行為發生于avoided之前，所以條件狀語從句使用的是過去完成時had known。