Which of the Solenoids Described Below Has the Greatest Magnetic

Multiple Choice

Which of the solenoids described below has the greatest magnetic field along its axis?

A) a solenoid of length L, with N turns and a current I
B) a solenoid of length L, with N/2 turns and a current I
C) a solenoid of length L/2, with N/2 turns and a current I
D) a solenoid of length 2L, with N turns and a current I/2
E) a solenoid of length 2L, with 2N turns and a current 2I