Which word signals a nonrestrictive clause in a complex sentence? a) that b) which c) while d) yet

Read the excerpt from the land. of my brothers, i was closest with robert. i suppose, in part, being the same year's children made us close, but there were other things too. we had been together practically since birth, and we always took care of each other. when i got into trouble, robert was there to pull me out of it if he could, or at least to see me through it, and i did the same for him. the passage provides evidence of why paul and robert have physical conflicts. paul and robert avoid social conflicts. paul is the least influenced by robert. paul is motivated to ask robert for .