As soon as I got home, I ran to my mother and asked, "Mom, do you have a 1 liter bottle?" Mom said, "There are 1 liter bottles in the cupboard." I searched for a while and finally found the cupboard. I opened the cupboard and there was indeed a bottle of 1 liter. I put the bottle under the tap and opened it. After the water was filled, I put 1 liter of water in my hand and weighed it. It's really light. I poured water into my cup, just enough for 4 cups, so it can be inferred that the capacity of each cup is 650. Later, I also did a milliliter experiment. I only dropped 13 drops of water and 1 ml, which means that 1 ml is rare. The total blood volume of healthy adults is about 4000 ~ 5000 ml. Usually about 3200 ~ 4000 ml of blood circulates in the heart and blood vessels, and about 800 ~ 1 000 ml of blood is stored in organs such as liver and spleen. The amount of unpaid blood donation is generally 200 ml.
The mystery in mathematics is really amazing!