The persistence of corpus luteum during pregnancy is due to a hormone known as

Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?

Select the correct pairs of germ layers and their derivatives from the following; and choose the correct option given below.

Germ layer	Derivatives
$a$. Mesoderm	All types of muscles of body
$b$. Ectoderm	Iris Muscles and Ciliary Muscles
$c$. Endoderm	Lining of Middle ear
$d$. Ectoderm	Adrenal cortex and Medulla
$e$. Mesoderm	Sclera and Choroid layer of eye

In mammals,the chorion and the allantois together form:

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.

Gestation period is the duration