题目

D For several days I saw little of Mr. Rochester. In the morning he seemed very busy with business，and in the afternoon gentlemen from the neighborhood called and sometimes stayed to dine with him. When his foot was well enough，he rode out a great deal. During this time，all my knowledge of him was limited to occasional meetings about the house，when he would sometimes pass me coldly， and sometimes bow and smile. His changes of manner did not offend me, because I saw that I had nothing to do with the cause of them. One evening，several days later，I was invited to talk to Mr. Roches 小明家的苹果树枝繁叶茂，却在形成花蕾以后出现落蕾现象。小明根据所学生物学知识及时给苹果树施加了适量的化肥以后，就不再出现落蕾现象，并且不久开花了。请问小明施加的化肥是： [　　] A．氮肥 B．磷肥 C．钾肥 D．氮肥和钾肥