Answer :
answer is B because the size of the orgamisum matters
Answer B seems to be logical. One cell is tiny and therefore vulnerable. Multicellular organism develops different kinds of tissues, which are built by specialized cells eg. skin cells that prevent damage. is the maintaining of structure so easy though? certainly it depends. BUT due to the fact that multicellular organism contains several types of cells, all these cells could perform different functions. so overally considering, answer D also makes sense. I'd say D is better answer but i am not 100% sure.