The Sun keeps shining a) mostly by gravitation contraction b) mostly by chemical reactions c) by converting hydrogen to helium. d) by converting hydrogen to carbon. e) by E = mc2. f) by F=G M_1 M_2/R12

C) by converting hydrogen to helium.

Explanation:

The Sun keeps shining because of nuclear fusion processes, which consists in creating helium atoms by combining hydrogen atoms, of an atomic mass less that of helium, in conditions of high core pressure and temperature. In other words, the Sun keeps shining by producing helium at the expense of its hydrogen reserves.

Therefore, the correct answer is C.

може ли да зареждате повече информация, моля

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.