他在看书译：he reading a book,he reading the book ,哪个对,why?

题目

他在看书译：he reading a book,he reading the book ,哪个对,why?
他在看书译：he reading a book,he reading the book ,he reading book哪个对,why?

答案

He is reading a book.
现在进行时：主语+be动词+动词ing形式.