The answer is B. 25°C.
A temperature of 25°C can be considered as a room temperature. It is an optimal temperature for the most living beings which cell potential is considered as standard. It is known that at 100°C water boils, so this temperature cannot be standard, cells will degrade at this temperature. Similarly 0°C and –273°C are too cold, water of the cells will freeze, cells will freeze, and cell potential will not be optimal.
An atom consists of an atomic nucleus composed of positively charged protons and neutral or uncharged neutrons.
There are different star systems. Binary star systems consist of two stars. Multiple star systems consist of two or more stars. The meaning of star system is "A small number of stars."
I think it's either A) a group of hundreds of stars, or B) a group of two or more stars. I would assume it's B), but i could be wrong.
Hope this helps!
