The correct option is D 2.0−2.5oC lower than the normal body temperature.
To ensure the survival and growth of the sperms, testes have been placed outside the abdominal cavity within a pouch called scrotum so as to ensure the optimal temperature. The scrotum helps maintain the low temperature (by about 2-2.5 degrees than the normal body temperature) required for spermatogenesis.
So, the correct option is '2.0−2.5o C lower than the normal body temperature'.