**Cells are capable of performing:**

**a) Synthesis:**
Cells are capable of performing synthesis, which refers to the process of building complex molecules from simpler ones. This includes the synthesis of proteins, nucleic acids, carbohydrates, and lipids. Proteins, for example, are synthesized through a process called protein synthesis, where amino acids are linked together to form a polypeptide chain. This synthesis of molecules is essential for the growth, repair, and functioning of cells.

**b) Respiration:**
Cells are also capable of performing respiration, which is the process of converting nutrients into usable energy. This energy is necessary for various cellular activities, such as movement, metabolism, and maintaining homeostasis. Respiration can occur through aerobic or anaerobic pathways. In aerobic respiration, cells use oxygen to break down glucose and produce ATP (adenosine triphosphate), the energy currency of the cell. Anaerobic respiration, on the other hand, occurs in the absence of oxygen and produces less ATP.

**c) Digestion:**
While cells do not have a digestive system like humans, they are capable of performing digestion at a cellular level. This cellular digestion, also known as intracellular digestion, involves the breakdown of large molecules into smaller ones within the cell. For example, during the process of phagocytosis, cells engulf and digest foreign particles or microorganisms. The cell membrane surrounds the particle forming a vesicle, which then fuses with lysosomes containing digestive enzymes. These enzymes break down the engulfed material into smaller molecules, which can then be used by the cell for energy or other cellular processes.

**d) All of these:**
The correct answer is option 'D' - all of these. Cells are capable of performing synthesis, respiration, and digestion. These processes are essential for the survival and functioning of cells, allowing them to maintain homeostasis, grow, reproduce, and carry out their specialized functions within multicellular organisms.

D, because a cell is the basic unit of life, when a group a cells stay together they form a tissue then the tissues form organs then the organs form a system then an organism like human, plants,etc. so therefore cells control every activity in an organisms' body because everything in our body is made of cells.