What are the three principal sources of the internal heat of terrestrial planets?

A) conduction, differentiation, and accretion.

B) accretion, differentiation, and radioactivity.

C) accretion, differentiation, and eruption.

D) convection, differentiation, and eruption

which of the following statements about the cosmic background radiation is not true?

(a) It has a temperature of about 3 degrees K about absolute zero.

(b) It is the result of moisture of radiation from many independent sources, such as stars and galaxies.

(c) It had a much higher temperatures in the past.

(d) It is isotropic.

The spectra of most galaxies show redshifts. This means that their spectral lines
(a) always are in the red part of the visible spectrum.
(b) have wavelengths that are longer than normal.
(c) have a higher intensity in the red part of the spectrum.
(d) have wavelengths that are shorter than normal.