You've moved the sentence, but now that you look at it, you're not happy with the change. Fortunately, you don't have to go through the entire cut-and-paste process again to move the sentence back. Instead, use Undo.
On the Quick Access Toolbar at the very top of the window, click the arrow on the Undo button . Move the insertion point over the last two actions, Paste and Cut, and then click. This will undo the last two actions you took, and place the sentence back in its original location. Or, to use another handy keyboard shortcut, press CTRL+Z twice to do the same thing.