About 300 b. c., aristarchus suggested that the sun was at the center of the universe. why?

the brightness of the planets would change.
the planets appeared to move among the constellations.
the planets always moved opposite to the stars.
the planets disappeared periodically.

The correct answer is option A and B

About 300 B.C., Aristarchus suggested that the sun was at the center of the universe because a) the brightness of the planets would change and b) the planets appeared to move among the constellations.

18 centuries before  Copernicus, Aristarchus predicted that  all planets orbit the sun. In other words, he suggested the Solar System is heliocentric.

answer: e.   sour taste

explanation: acids are those substances which dissociates in water to give ions. as they dissociate to give ions, they act as electrolytes and thus are electrically conductive. acids are sour in taste. example: hcl

bases are those substances which dissociates in water to give ions or accepts ions. as they dissociate to give ions, they act as electrolytes and thus are electrically conductive. bases are bitter in taste. bases are slippery in nature.