Sometimes the separation of twins is incomplete and they are born attached and remain so even after birth. Such twins are known as:

Progesterone is secreted by.........

Cleavage is a unique form of mitotic cell division in which

Find the correct statements :
$A.$ In human pregnancy,the major organ systems are formed at the end of $12$ weeks.
$B.$ In human pregnancy the major organ systems are formed at the end of $8$ weeks.
$C.$ In human pregnancy heart is formed after one month of gestation.
$D.$ In human pregnancy,limbs and digits develop by the end of second month.
$E.$ In human pregnancy the appearance of hair is usually observed in the fifth month.
Choose the correct answer from the options given below.

Which hormones show an increased level in the maternal blood during pregnancy?

What is the cavity of the gastrula called?