Which of the following statements about a bacterial cell is/are correct?
$(i)$ Mesosome is formed by the extensions of plasma membrane into the cell.
$(ii)$ The pili are elongated tubular structures made up of a protein.
$(iii)$ Flagellum is composed of filament,hook,and basal body.
$(iv)$ Ribosomes are about $30 \; nm$ by $50 \; nm$ in size.

• A
  $(i), (ii)$ and $(iii)$
• B
  All of the above
• C
  $(ii)$ and $(iv)$
• D
  None of the above