Lymph can be defined as:
Lymph is a clear fluid that circulates throughout the lymphatic system. It is composed of various substances that have been filtered out of the blood, including water, proteins, fats, and white blood cells (WBCs). Lymph plays a crucial role in maintaining fluid balance, transporting nutrients, and removing waste products from tissues.

The correct answer is option 'D' (Blood minus RBC and Platelets).

Explanation:
Lymph is derived from blood plasma, the liquid component of blood. However, it differs from blood plasma as it lacks red blood cells (RBCs) and platelets. Let's understand why lymph does not contain RBCs and platelets:

RBCs:
Red blood cells, also known as erythrocytes, are responsible for carrying oxygen to body tissues and removing carbon dioxide. They are produced in the bone marrow and remain in the bloodstream. However, they cannot pass through the walls of the capillaries into the lymphatic vessels. Therefore, lymph does not contain RBCs.

Platelets:
Platelets, also called thrombocytes, are essential for blood clotting. They are involved in the formation of blood clots to prevent excessive bleeding. Platelets are also unable to cross the capillary walls and enter the lymphatic vessels. Hence, lymph does not contain platelets.

Composition of Lymph:
Lymph primarily consists of:
- Water: Lymph is mainly composed of water, which makes up the majority of its volume.
- Proteins: Lymph contains various proteins, including albumin and globulins. These proteins help maintain osmotic pressure and transport substances.
- Fats: Lymphatic vessels in the digestive system, called lacteals, absorb dietary fats. These fats are transported in the form of chylomicrons within the lymph.
- White Blood Cells (WBCs): Lymph is rich in white blood cells, including lymphocytes and macrophages. These immune cells play a crucial role in defending the body against infections and foreign substances.
- Other substances: Lymph also contains dissolved gases, hormones, metabolic waste products, and cellular debris.

Functions of Lymph:
- Fluid balance: Lymph helps maintain fluid balance by returning excess interstitial fluid back into the bloodstream.
- Immune response: Lymph transports immune cells, such as lymphocytes, to areas of infection or inflammation.
- Nutrient absorption: Lymphatic vessels in the small intestine absorb dietary fats and fat-soluble vitamins, transporting them to the bloodstream.
- Waste removal: Lymph carries metabolic waste products and cellular debris away from tissues for elimination.

In conclusion, lymph is a fluid derived from blood plasma that lacks RBCs and platelets. It consists of water, proteins, fats, and white blood cells and plays vital roles in maintaining fluid balance, immune response, nutrient absorption, and waste removal.

Lymph is tissue flood it contains only white blood cells.
so option D is correct.