Which of these is equivalent to the law of conservation of energy?
a. the total mechanical energy is always conserved.
b. friction is a nonconservative force.
c. kinetic energy can be transformed into thermal energy.
d. the total energy of all types remains the same in a closed system.

The correct option A.

Explanation:

Mechanical energy is defined as the sum of the both potential and kinetic energies.

M.E = P.E + K.E

So, from the given options the correct answer is option A.

they are non-matter

explanation:

they are non-matter. basically, any type of energy or any abstract concept is an example of something that does not matter. other examples include dreams, magnetism, radio, and hate

the second one and the forth one are in the purple because they are opinions and the rest are in the yellow

explanation: