题目

右图表示不同浓度生长素对芽生长的影响。当植物表现出顶端优势时，顶芽和最靠近顶芽的侧芽所含生长素的浓度依次分别为 A．a和b        B．b和a       C．b和c        D．c和b 答案：C —Why not take this road? It’s a short cut.     — I am afraid we can’t. It _____. A. is repaired         B. is being repaired  C. has repaired       D. is repairing