That must be a lot more fun than taking a bus的句子成分分析

句子的主语是that,谓语是must be,宾语是fun.补足语是a lot more和than taking a bus.
在这个句子中,a lot是用来修饰比较级more的,a lot more加在一起,用来修饰fun.而than taking a bus,则是宾语fun的后置定语.
整个一句话,采用的是比较级的句式,翻译应为“那一定要比做汽车有意思多拉!”