Answer: Option A
:
A and B
The strength of the magnetic field generated by a solenoid can be increased by:
(i) Increasing the number of turns per unit length. The more the number of turns in a solenoid, the stronger is the magnetic field produced.
(ii) Increasing the electric current. The larger the current passed through the solenoid, the stronger is the magnetic field produced. 
(iii) The nature of the core material used. Using soft iron as the core in the solenoid, increases the magnetic field strength.
However, the field strength does not depend on the mass or the density of the coil material.