In order to get her 3 rd grade students to memorize the poem written on the chalkboard, Mrs. Thyberg gives the students stickers for each poem they can recite from memory. After earning 5 stickers, a student gets to pick a prize out of the goody box. Mrs. Thyberg is using a(n) to modify the children's behaviors.

Read the passage from sugar changed the world. sugar is a taste we all want, a taste we all crave. people throughout the planet everywhere have been willing to do anything, anything at all, to get that touch of sweetness. we even know exactly how thrilling it was to taste sugar for the first time. when the lewis and clark expedition met up with the shoshone, who had little previous contact with old world products, sacagawea gave a tiny piece of sugar to a chief. he loved it, saying it was "the best thing he had ever tasted." sugar created a hunger, a need, which swept from one corner of the world to another, bringing the most terrible misery and destruction, but then, too, the most inspiring ideas of liberty. sugar changed the world. we begin that story with a man who could never know enough. how does the conclusion of the prologue support the authors’ purpose? select two options. it introduces the topic that will be addressed next. it provides information about the authors. it states why the topic is relevant to readers. it cites sources the authors used in the text. it explains how the authors came to study the subject.