What causes the differences in physical characteristics like hair color among people? different versions of genes variations in dna length different numbers of chromosomes variations in cell nucleus size

First option, different versions of genes.

Explanation: Things like skin color, hair color, height and a lot of other things that you maybe can't see at plain sight (Like genetic diseases and such things) are totally determined by your genetics (which are passed from parents to their childs, and this is why they have similar traits), this means that the right answer is Different versions of genes.

different numbers of chromosomes

explanation:

newton's third law, for every action there is an equal and opposite reaction.

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia