副词.类似于 absolutely,意思是真正地、确实、完全.
例如：I just can't take it anymore.我实在是再也无法忍受了.
he was just grand as Romeo 他确实是和罗密欧一样出色.
it's just beautiful.实在是太美了!
你给的例句可翻译成：我的确作业太多,我真不知道该先做哪一个.