The magnetic induction produced inside an ideal solenoid depends on which of the following quantities?
$(a)$ Number of turns per unit length $(n)$.
$(b)$ Radius of the wire.
$(c)$ Current flowing through it $(I)$.
$(d)$ Permeability of the medium $(\mu)$.

• A
  $(a)$, $(c)$ and $(d)$
• B
  $(a)$, $(b)$ and $(c)$
• C
  $(b)$, $(c)$ and $(d)$
• D
  $(a)$, $(b)$ and $(d)$