题目

—Thank you for your help，Sarah． —_____________.( 浙江台州) A．Good idea               B．Please don't say so    C．It doesn't matter    D．You are welcome 答案：D解析：Thank you!的答语往往用You are welcome，Not at ail，That's all right等。有机物常用键线式表示其结构简式，比如表示2-甲基丁烷，则所表示的有机物的分子式为______．