题目

I arrived at school late yesterday.(变否定句) I________at school late yesterday. 答案：【答案】didn't arrive【解析】谓语arrived是一般过去时，变为否定句，用助动词didn't，后面接动词原形arrive。故填didn't arrive。醛类因易被氧化为羧酸而使酸性高锰酸钾或溴水褪色．现已知柠檬醛的结构简式为：，若要检验其中的碳碳双键，请你设计实验方案______．