Earth is taken as zero electric potential, through it has net negative charge because of a. its layer radius
b. its smaller radius
c. heavy mass
d. its large permittivity

"Its larger radius"

Explanation:

The electric potential is given by :

Where

k is the electrostatic constant

Q is electric charge

r is the radius

For Earth, the value of r is very large and Q is very smaller. Due to large r, the potential of Earth's surface is almost zero. Hence, the correct option is (a).

cell differentiation  is how generic embryonic  cells  become specialized  cells. this occurs  through a process called gene expression. gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and this is what dictates how a  cell  functions.

explanation:

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.