For convection to occur,
a. dark objects are required to absorb energy.
b. substances must be in contact with each other.
c. particles must be able to flow within a substance.
d. heat must transfer from an area of less energy to more energy.

C. Convection is the transfer of energy by the motion of a fluid. Fluids are by definition substances in which particles are able to flow. Hence the answer is c

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.