Cytokinesis usually begins after mitosis when the cell is ready to divide its cytoplasm. Out of the options provided, the correct answer is a) telophase.
During telophase, the chromosomes begin to de-condense, nuclear envelopes start to form around the separated sister chromatids, and it is at this stage that the mechanisms to divide the cytoplasm, known as cytokinesis, initiate. This process ensures that each daughter cell receives an adequate amount of organelles and cytoplasm, following the completion of mitosis.