Who can analyze this English sentence?

题目

Who can analyze this English sentence?
Doubtful as to what might be in store for him,Julien had left home in the dead of night.
这是个什么句型?

答案

(As he was )doubtful as to what might be in store for him,Julien left home in the dead of night
由于省略了括号中的部分,doubtful as to what might be in store for him就成了Julien -- - - - - 这个句子的表示伴随结构,修饰主语Julien ,做Julien的主语补足语.