What do folic acid supplements and iron supplements have in common? They are used together to treat cases of septicemia. Both are frequently prescribed for cases of anemia. They are used to maintain a healthy level of leukocytes. Both are often prescribed to inhibit platelet aggregation.

Iron and folic acid supplements are necessary and commonly used in the treatment of anemia. Clinical anemia is a condition due to decreased red blood cells, hemoglobin, or lack of iron.

Iron is an important part of hemoglobin, a molecule found in red blood cells that allows the transport of O₂ and CO₂ gases.
Folic acid is a necessary cofactor for the synthesis of new cells, including red blood cells or erythrocytes.

The joint use of folic acid and iron supplements in cases of anemia contributes to the formation of new erythrocytes and hemoglobin molecules, in addition to improving and preventing anemia by providing sufficient iron deposits for these cells to fulfill their function.

The other options are not correct because:

Antibiotics are used in septicemia.
Folic acid and iron are not related to the amount or health of the leukocytes.
Folic acid and iron are not used to inhibit platelet aggregation.