What does the word “this” in the last line refer to?

Read the quoted parts carefully and answer the questions in English. Write your answers in the corresponding space on the answer sheet.“Nor lose possession of that fair thou ow’st;/Nor shall death brag thou wander’st in his shade，/When in eternal lines to time thou grow’st: /So long as men can breathe，or eyes can see， /So long lives this,and this gives life to thee. ’’
What does the word “this” in the last line refer to?
【正确答案】：

“THIS”REFERS TO THE POEM. A NICE SUMMER'S DAY IS USUALLY TRANSIENT, BUT THE BEAUTY IN POETRY CAN LAST FOR EVER. 

【题目解析】：最后一行引号中的指示代词指的是这首诗。一个美好的夏日通常是短暂的，但诗歌中的美却可以永恒。