They use fans and air conditioning in the summer because its hot, which means they use energy and in the winter, there is no need because its cold so less energy.
B.
The cynobacteria were already there without the oxygen, so that rules out A, and a lot of prokaryotes were anaerobic, so that rules out C. Finally, Photosynthesis does not require oxygen. Instead, Oxygen is a waste product of it. Therefore, it cannot be D. So, we are only left with B
Hoped this helped :D
Answer:
The Earth, Stars, and Mars I guess...
Answer: 3 significant figures
Explanation: because in scientific notation only the before and after decimal number are considered but in standard form all numbers including exponents are all significant figures
Density is defined as the ratio of mass to the volume.
Density = 
(1)
Mass of water = 10 grams
Mass of acetone = 10 grams
Density of water = 1 
Density of acetone = 0.7857
Put the value of density of water and its mass in equation (1)
1 = 
Volume of water = 10 
Put the value of density of acetone and its mass in equation (1)
0.7857 =
Volume of acetone = 12.72
Thus, volume of acetone is more than volume of water because the density of acetone is lower.
