The number of chromosomes in a cell division is halved. This kind of cell division is observed in:

The chapter explains: "many multi-cellular organisms have found... to have special lineages of cells in specialised organs in which only half the number of chromosomes and half the amount of DNA as compared to the nonreproductive body cells [are present]. This is achieved by a process of cell division called meiosis." In humans, these germ-cells (sperms and eggs) are formed specifically in the testis (male) and ovary (female).

• (A) Only testis — incorrect. This ignores that the female reproductive organ, the ovary, also produces germ-cells (eggs) through the same halving (meiotic) division.
• (B) Only ovary — incorrect. Similarly, this ignores that sperm formation in the testis also involves this reductional division.
• (C) Ovary and testis both — correct. Both organs contain the specialised germ-cell lineages where meiosis halves the chromosome number, so that when the male and female gametes fuse during fertilisation, the normal (full) chromosome number is restored in the zygote.
• (D) All cells of the body — incorrect. Ordinary body (somatic) cells divide by mitosis, which keeps the chromosome number constant, not halved; only the specialised reproductive-organ cell lineages undergo the chromosome-halving division.