... banana (main clause) "the thing" is a common element (object of independent clause / subject of main clause), so you use a relative pronoun "that" or "which"...
...independent sentence,-------> If a clause can stand alone as a sentence, it is an independent clause.
好簡單，句子能獨立存在，咪叫independent clause。相反，句子不能獨立存在，咪叫dependent clause。 就好似： Because he was ill, he was absent. Because he was ill, = dependent clause he was absent. =independent clause