Final answer:
The matrix of loose connective tissue is produced by fibroblasts, which are not listed among the choices given, making the correct answer 'none of these choices'. The correct option is d.
Step-by-step explanation:
The matrix of loose connective tissue is produced by fibroblasts. These are the most abundant cells in connective tissue proper and they are responsible for secreting the fibers and other components of the connective tissue matrix, which includes ground substance and fibers such as collagen, reticular fibers, and elastin.
Although cells like macrophages, mast cells, and plasma cells are present in the connective tissue, they are part of the immune system and are not involved in the direct production of the extracellular matrix.
Therefore, the correct answer to the student's question is d) none of these choices since the options provided do not include fibroblasts, which are the actual cells responsible for producing the matrix of loose connective tissue. The correct option is d.