Respuesta :
The answer is probably B because white blood cells are part of the immune system, so help to fight diseases. The circulatory system helps to move the white blood cell around the body. Also, pathogens are disease causing organisms, and as you can see, they all relate very well. Hope i helped, have a nice day.
The correct is actually D , this is a question I have reviewed before in the past and the correct answer is def D as I remember clearly , I forgot how I explained it but I know for sure the answer is D :)
Have a merry Christmas !