Final answer:
It is true(A) that red and white blood cells and platelets are the formed elements of blood. Platelets are the formed elements that arise from myeloid stem cells among the given options.
Step-by-step explanation:
The formed elements of blood consist of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes). Answering the first question, it is true that red and white blood cells and platelets are the formed elements of blood. Regarding the second question on which of the formed elements arise from myeloid stem cells, granular leukocytes such as neutrophils, eosinophils, and basophils, as well as agranular monocytes and platelets, are produced from myeloid stem cells. Hence, the correct option is c. platelets, as other cells listed are derived from lymphoid lineages.