(But) it was hard for them to decide which was the most impo
(But) it was hard for them to decide which was the most important one,(so) they thought it would be best to just (start) playing ,using all the objects,and gradually get rid of what they had brought to see which was truly indispensable. 这段话中为什么But 和so 可以连用?start 之后的长句什么结构怎么翻译?