According to the NCERT textbook context: (a) T4 is a thyroid hormone, hence matched with Thyroid (ii). (b) PTH stands for Parathyroid Hormone, which is secreted by the parathyroid gland, hence matched with Parathyroid (iv). (c) GnRH (Gonadotrophin Releasing Hormone) is explicitly stated as 'a hypothalamic hormone' that stimulates the pituitary, hence matched with Hypothalamus (i). (d) LH (Luteinizing Hormone) is clearly mentioned as being produced by the pars distalis region of the pituitary gland, hence matched with Pituitary (iii).