go to bed earlier than （usual）还是（usually） 为什么

选usual
usually是副词,意思是通常,经常的意思
usual是形容词,意思是通常的；寻常的；惯常的



副词主要用来修饰动词,形容词,副词或其他结构.

形容词简单了,它修饰名词,说明事物或人的性质或特征.

以下是usual的几个例句：
He arrived late as usual.
他照常迟到.
It is below the usual size.
它不足一般尺寸.
After lunch there was a little more clearing up to do than usual.
午餐之后要做的清扫工作比平时略多.

记得区分关于usually的短语：more than usually 比平时更
She felt more than usually hungry after her excursion.
远足后,她比平时感觉更饿.
He was more than usually depressed by problems at work.
工作上的问题使他异常沮丧.