1.Joshua quickly finished his homework and went out to play.
Joshua是主语,finished和went是两个谓语,quickly是副词修饰动词finished,his homework是finished后面的宾语.
2.People（S） have thought about going into space for many years.
首先,people不能加S,have thought about是谓语,动名词短语going into space为宾语,for many years是时间状语.
3.What is the most expensive meal listed on the menu?
是个特殊疑问句,what是疑问代词,作主语；is是系动词,作谓语；meal是表语；the most expensive和listed on the menu作为定语修饰meal.