请分析下这两个英语句子的成分

1.I spent two weeks in reading this book.
句中 this book是reading的宾语；reading this book是介词in 的宾语.in也可以省略,这样in reading this book 做spent 的宾语补足语.
2.Rex soon became an expert at opening the gate.
句中opening是动名词,因为在介词后面,必须具有名词性质,故动词名词化了.