Obstinate simply means to be resistant to change. An obstinate person will stubbornly adhere to his or her opinion,
despite persuasion it arguments
Such person will refuse to change their mind or be convinced to do something that they do not want to do. Some synonyms of obstinate include mulish, dogged, stubborn etc
The answer to your question is A. - Them because you are referring to the crumbs and just not something random, in which case you would use "it". I hope this helps you! Have a great day!!