Modifications, particularly the presence of the loop of henle, allow mammals and birds to reabsorb water efficiently and produce a urine

The answer is hyperosmotic urine.

A counter current mechanism system refers to a process, which spends energy to produce a concentration gradient. It is witnessed broadly in nature and mainly in mammalian organs. For example, it can signify towards the process of urine concentration, that is, the generation of hyperosmotic urine.

The hyperosmotic urine exhibit greater osmolarity in comparison to the blood. The kidneys generate hyperosmotic urine in response to a deficiency of water as an effort to return to homeostasis.

rain is the best answer

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.