Something that is best stationary & is used to see if another object is in motion.

the answer to this is proletariats.

hope this : )

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.