Why Are Cytotoxic Medications Administered in Cycles with Periods of No

Why are cytotoxic medications administered in cycles with periods of no administration in between?

A) To allow a patient's system to accumulate the effect of cytotoxic medication over subsequent administrations
B) Because cytotoxic agents also destroy noncancerous cells,and the body needs time to recuperate lost cells to avoid or decrease potential adverse effects
C) To allow the cytotoxic agent more careful selection of the targeted cancerous cells,which increases its effect
D) To allow the patient a rest period in which to take noncytotoxic agents that may otherwise have cross-reactions