Which is a simple sentence?

 - According to many scholars, the 1798 publication of Lyrical Ballads by Samuel Taylor Coleridge and William Wordsworth began the romantic period in English literature.
 - Lorenzo picked raspberries in the field until his fingertips were stained red.
The second sentence is the simple sentence. It is a single independent clause.
According to many scholars, the 1798 publication of Lyrical Ballads by Samuel Taylor Coleridge and William Wordsworth began the romantic period in English literature.