Select the correct answer. Which of the following happens during the main-sequence stage of a star's life?
A. It cycles, appearing brighter and dimmer in turns,
B.
it changes the color that it emits,
It increases its distance from the Sun.
D.
It grows continuously smaller and dimmer,

Ithink your answer is d

What formula  this one  (x_/

Because the sun is the biggest and if the sun orbits the earth we will be dead probably

If the heat engine is a perfect carnot cycle engine, thenefficiency = (t2-t1)/t2   where t1=temperature of cold reservoir ( ° k) = 135            t2=temperature of hot reservoir ( ° k)   = 325thereforeefficiency = (t2-t1)/t2 = (325-135)/325 = 0.5846 = 58%  note: this is the theoretical maximum efficiency of a perfect heat engine.   real-life engines do not achieve this value.