题目

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 (66) When a person does a certain thing again, he is impelled(迫使) by some unseen force to do the same thing repeatedly; thus a habit is formed. Once a habit is formed, it is difficult, and sometimes impossible, to get rid of. (67)  Children often form bad habits, some of which remain with them as long as they live. Older persons also form bad habits as long as they live. Older persons also form bad habits, and sometimes become ruined by them. (68) Many successful me不同浓度的生长素影响某植物乙烯生成和成熟叶片脱落的实验结果如下图所示。下列叙述错误的是A．乙烯浓度高脱落率不一定高B．一定浓度的生长素可以促进乙烯的生成C．生长素和乙烯对叶片脱落的作用是相似的D．生产上喷施高浓度生长素类似物可提高脱落率