The thymus is a lobed organ located near the $...A...$ and beneath the $...B...$. The most appropriate combination for $A$ and $B$ is:

The thymus gland develops from the embryonic ..........

Select the correct statements regarding Thymus gland.
i. It is located in the upper part of thorax.
ii. It is made up of four lobes of lymphoid tissue.
iii. It is a prominent gland formed at birth and remains active throughout life.
iv. It is also called temporary gland.
v. It plays an important role in the development of immune system and provides humoral immunity.
In the light of above statements,choose the correct option from below.

$T-$ lymphocytes are:

Mammalian thymus is mainly concerned with

The size of this organ is large at the time of birth,but it gradually shrinks as age increases.