Which of these is a concept the romantics valued?
a. idleness
b. imperialism
c. innocence
d. industrialism

Innocence is a concept of the romantics that is valued

The so-called "Dark Romantics" notwithstanding, the best answer would be

C. Innocence

William Blake, although considered a "Pre-Romantic," wrote a book of poetry entitled, "Songs of Innocence and of Experience" --  in which he wrote

"Piping down the valleys wild Piping songs of pleasant glee 
On a cloud I saw a child. 
And he laughing said to me. 

Pipe a song about a Lamb; 
So I piped with merry chear, 
Piper pipe that song again— 
So I piped, he wept to hear. 


...And I wrote my happy songs Every child may joy to hear"

This typifies Romanticism, in that the child, like the "Noble Savage"-indigenous peoples in pre-industrializing areas of the 18th- and-19th-centuries, remains in an effectively "unspoiled" state of being.