Respuesta :
The phrase to look closely is the correct choice. If you add the words look closely into the line, it reads Look closely at the lines, making it correct.
Answer:
To look closely
Explanation:
The 5th line is: "Search narrowly the lines!—they hold a treasure"
Narrow means limited or restricted. As an adverb, though, Narrowly means "with close adherence, by a narrow margin, closely". It means that when you're narrowly searching, you're doing a very close search.