【正确答案】 A

【答案解析】[注释] 首段第二句In this world，a child's wildest thoughts would become reality， limited only by the extent of his or her imagination．是本题的依据。其中this world就是上一句提到的(Imagine)a world in which...；the extent of his or her imagination意思同答案 A．the limits of their imagination。