**Core Concept**
Haemophilia A and Von Willebrand's disease are two of the most common inherited bleeding disorders. They are caused by deficiencies or abnormalities in specific proteins involved in blood coagulation.

**Why the Correct Answer is Right**
Haemophilia A is caused by a deficiency of factor VIII, a clotting factor essential for the intrinsic pathway of blood coagulation. Von Willebrand's disease, on the other hand, is caused by a deficiency or abnormality of von Willebrand factor (VWF), a protein that plays a crucial role in platelet adhesion and the stabilization of factor VIII. The loss of functional VWF leads to the degradation of factor VIII, resulting in a deficiency of this critical clotting factor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify the correct factor involved in haemophilia A and Von Willebrand's disease.
**Option B:** This option is incorrect as it is not the primary cause of either haemophilia A or Von Willebrand's disease.
**Option C:** This option is incorrect as it is not directly related to the pathophysiology of haemophilia A and Von Willebrand's disease.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that haemophilia A and Von Willebrand's disease are the most common inherited bleeding disorders and are caused by deficiencies or abnormalities in clotting factors VIII and VWF, respectively.

**Correct Answer:** D. Deficiencies or abnormalities of clotting factors VIII and von Willebrand factor.