<prompt> In semen banks, semen is preserved at low temperature using:Dry iceDeep freezeLiquid nitrogenLiquid air  <response>: Ans. is c, i.e. Liquid nitrogenRef: Jeffcoate 7thed, p723Cryopreservation of semen:Involves cooling of embryos in the pronucleate stage or early cleavage stage to very low temperature in the presence of cryoprotectants such as: I2 - Propanediol Iodine Glycerol Dimethyl sulphoxide DMSO with sucrose. They are then stored in liquid nitrogen till required.Q Over half the embryos survive thawing process. 