题目

 —You’d better _________ some popcorn or soft drinks before the film begins.—But I think it’s better _________ anything while watching the film.A. buy; not have                                B. to buy; not to have  C. to buy; not have                            D. buy; not to have 答案：D小涵同学利用如图所示装置研究电和磁的关系，请仔细观察图中的装置、操作和现象，然后归纳结论：（1）比较甲和乙可知：    ；（2）比较    可知：电流的磁场方向与电流方向有关．