D. 1,200
This is because if it takes 1 and a half hours **1.5** to travel through city a and city b , and the plane goes 800km per hour and 400km is half of that it then the answer has to be d.
Different types of blood contact different kinds of antigens and antibodies. For example, Type A blood has A antigens and B antibodies, antibodies being the thing that fights B antigens. Type B blood has B antigens and A antibodies. So if someone with type B gets transfused with Type A blood, the person's antibodies will attack the new blood.
They don't use anything. Water and nutrients move through the plants body cell by cell.