Which type of innate barrier does the $Stratum$ $corneum$ represent?

Which of the following is a characteristic of antibodies?

Identify the correct statements from the following:
$(i)$ The skin is the main physical barrier.
$(ii)$ Mucus coating of the epithelium lining the respiratory,gastrointestinal,and urogenital tracts is a physiological barrier.
$(iii)$ $IgA, IgM, IgE, IgG$ are types of $T$-cells.
$(iv)$ The primary immune response is very intense.

Passive immunity was discovered by

$..........$ produces an army of proteins in response to pathogens into our blood to fight with them $:-$

Graft rejection is caused by which of the following?