What is produced by sensitized helper $T$-cells?

Which of the following statements is false?

Which memory cells are produced during vaccination?

Which of the following statements is incorrect?

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.

In which of the following organs do immature lymphocytes differentiate into antigen-sensitive lymphocytes?