Lincoln came from nothing, yet but he did ____ that changed the world.

Creating better health care, education and housing for everyone is a simple idea, but ____ which is hard to put into practice．

(2013·山东济宁模拟)When you are done with the book, go out for a walk or ________.

The schoolboys and schoolgirls are walking along the street, _____a small redcap .

--- Who has eaten all the cake, Jim?  --- Oh,       must be your two pet dogs.