In 1915 Niels Bohr proposed a model of an atom that modified an earlier model. Based on quantum mechanics, the Bohr model is called a planetary model, as it shows electrons with a negative charge (i) _______ a nucleus, which has a positive charge. Bohr suggested a(n) (ii) ________ relationship between gravitational forces in the solar system and the electrical force between positively charged nucleus and negatively charged electrons.

Blank (i)	Blank (ii)
A. envelops	D. analogous
B. converges	E. homologous
C. orbits	F. retrogression