$MALT$ constitutes about ................. of the lymphoid tissue in the human body. (in $\%$)

Read the following statements and choose the correct set of statements $:$
$(a)$ Cell-mediated immune response is responsible for the graft rejection.
$(b)$ Grafts from just any source $-$ an animal,another primate,or any human beings can be made since the grafts would be accepted sooner or later.
$(c)$ The organs cannot be taken from just anybody for transplant.
$(d)$ Tissue matching,blood group matching are essential before undertaking any graft/transplant.
Choose the correct answer from the options given below $:$

In the case of tetanus,a patient is directly injected with antitoxins. This type of immunity is called .........

Which of the following statements is correct regarding immunity?

$A$ boy happens to put his foot on a rusted nail and the doctor gives him an injection. Most likely,what has the doctor administered?

Which cells help $B$-cells in the production of antibodies?