keep on a diary 还是keep a diary

要表达写日记时，正确的表达形式是keep a diary，例如Do you have a good habit of keeping a diary?你有写日记的好习惯吗？Keep on a diary意思是保留着一个日记本，My mother kept a diary in the old desk，在这张旧书桌里面，我妈妈保留着一个笔记本。