给出一段英文文本，将其中的情态动词（如could、should、might）转换为它们的过去式形式。输出转换后的文本。


Can you help me carry these boxes?
You should eat more vegetables.
They might arrive late.
Could -> Could not / Couldn't
Should -> Should not / Shouldn't
Might -> Might not / Mightn't

转换后的文本如下：

Can you help me carry these boxes?
You should eat more vegetables.
They might arrive late. 

变成：

Can you help me carry these boxes?
You couldn't  help me carry these boxes?
You shouldn't eat more vegetables.
They mightn't arrive late.