Which statement is true?

the earth's moon is thought to have formed when a mars-sized planet collided with earth during its final stages of planetary accretion.
without the earth's moon, life on earth would not be possible.
the earth's moon is the smallest moon relative to its host planet.
the earth's moon is the same size as the earth.

The magnitude of the magnetic field at a certain distance from a long, straight conductor is represented by b. what is the magnitude of the magnetic field at twice the distance from the conductor? a. at twice the distance, the magnitude of the field is 4b.b. at twice the distance, the magnitude of the field is 2b.c. at twice the distance, the magnitude of the field is b/2.d. at twice the distance, the magnitude of the field is b/4.e. at twice the distance, the magnitude of the field remains equal to b.