依然是新概念3第十课的问题'Four days after setting out ,while the Titanic

依然是新概念3第十课的问题
'Four days after setting out ,while the Titanic was sailing across the icy waters of the North Atlantic ,a huge iceberg was sudddenly spotted by a look-out .'“Four days after setting out”和“while the Titanic was sailing across the icy waters of the North Atlantic”可否合为一个定语从句来说?