Question

The author credited with launching the English romantic movement was

Answer 1

The author credited with launching the English romantic movement was "William Wordsworth" especially with his masterpiece "The Prelude", although it should be noted that there several other prominent, early romantic writers. 

Answer 2

The most likely answer you're looking for:  William Wordsworth.

Depending on who/what was covered in your classroom, it's also possible that Samuel Taylor Coleridge could be mentioned together with Wordsworth as the early leaders of the Romantic movement in England. The two of them together are often credited with launching the English Romantic movement.  Wordsworth and Coleridge were friends and sometimes collaborators.  Interesting Literature (a site based in England), has listed their picks for "10 of the Best Poems by English Romantic Poets," and the top 4 on their list are by Wordsworth and Coleridge:

1. My Heart Leaps Up (by Wordsworth)

2. I Wandered Lonely as a Cloud (by Wordsworth)

3. Frost at Midnight (by Coleridge)

4. The Rime of the Ancient Mariner (by Coleridge)