David comes into the emergency room late at night with a cut that will not stop bleeding. His mother, Rose, is worried that he has a bleeding disorder, just like his grandfather. The lab is closed, so the doctor cannot order a specialized coagulation test. However, the hospital does have a sample of blood from a classic hemophiliac. What is the simplest test the doctor could perform using David's blood to determine if it is missing factor VIII activity

The doctor can mix a blood sample from the hemophiliac patient with David's blood.

Explanation:

This test is called Mixture Test and is performed quickly when there is no time to do more detailed and accurate tests. In the mixture text, two blood samples are mixed, where one is from a patient with hemophilia. when mixing the two samples, the doctor observes whether there were coagulation inhibitors in the patient's blood, and can then draw conclusions about the presence of hemophilia in the patient.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.