What is the structure of the bipolar spindle composed of?

Select the correct option on the basis of the following events:
$(I)$ Chromosomes cluster at opposite spindle poles.
$(II)$ Nuclear envelope assembles around the chromosome clusters.
$(III)$ Golgi complex and $ER$ reform.

Chromosomes become long and thin,eventually turning into chromatin material,and the nucleolus and nuclear envelope reappear. In which phase are these changes observed?

After which phase of interphase does the cell enter into mitosis?

In which phase do new nuclei come into existence?

In which phase do the sister chromatids separate?