The correct option is D Forming a manchette.
Sertoli cells are 'nurse' cells, which is a part of a seminiferous tubule and helps int he process of spermatogenesis i.e., production of sperms.
Sertoli cells are secretory cells. One of the substances which it secretes is inhibin which is secreted after puberty and work together to regulate FSH regulation.
Sertoli cells continuously secrete fluid that is used for the sperm transport is proximal genital ducts.
Manchette is a conic array of microtubules that invests the nucleus of a spermatid. It plays a role in shaping the nucleus during spermatogenensis.
Thus, the correct answer is option C.