4，Three day after Rastus' disappearance, Mrs. Ramsay received an anonymous letter.

after可以和名词搭配 e.g. three days after arrival

an anonymous letter 匿名信

5，The writer stated that Rastus was in safe hands and would be returned immediately if Mrs Ramsay paid a ransom of &1000.

state 非常正式的声明新概念英语第三册mp3

in safe hands 在可靠的人手中，意指“很安全”

 6，Mrs. Ramsay was instructed to place the money in a cardboard box and to leave it outside her door.

be instructed to do sth. 受指示做某事

e.g. The journalist was instructed to obtain the so-called important statistics.

7, At first, she decided to go to the police, but fearing that she would never see Rastus again --the letter had made that quite clear--she changed her mind.

fearing 现在分词做原因状语

 make it clear to sb. that

e.g. The teacher has made it clear to us that we must read English aloud every day.