The question asks for the standard treatment of iron deficiency anemia in pregnancy. Rather than naming the drug directly, let's evaluate each option by what it actually treats or supplies, and how appropriate that is for routine use in pregnancy.
Since the question asks for the standard treatment (not a special-case one), and only ferrous sulphate is the conventional, first-line oral iron replacement used routinely, it stands out as the answer, with folic acid ruled out for treating a different deficiency and the injectable/other iron forms ruled out as non-first-line options.
Therefore, the correct answer is Ferrous sulphate.