Horses and zebras can be bred to produce a zorse, which is infertile. Which is most likely the reason zebras and horses are considered separate species?
They cannot breed.
Their offspring cannot breed.
They look different from each other.
They are found in different habitats.

The correct option is B) Their offspring cannot breed.

Explanation:

Organisms belonging to the same species require the ability to breed and produce fertile offsprings. If two organisms breed to produce infertile offsprings, then they are not considered to belong in the same species. Infertile offsprings do not have the capability to reproduce. The breeding between a horse and a zebra produces zorse, which is sterile. This depicts that both the zebra and horse belong to different species as they cannot produce a fertile offspring.

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.