The correct option is C Mesoderm
After implantation, the inner cell mass (embryo) differentiates. The human foetus within the uterus, develops into an outer layer called ectoderm and an inner layer called endoderm. A mesoderm soon appears between the ectoderm and the endoderm. These three layers give rise to all tissues and organs in in the growing embryo. Gonads, muscles, dermis, kidneys etc. develop from the mesoderm.