The data bus is Bi-directional because the same bus is used for transfer of data between Micro Processor and momory of input / output devices in both the direction.
Albedo refers to a material's ability to reflect sunlight. Since 30% of the sun's energy is reflected by the entire earth, the earth has an average albedo of 0.30.
Generally, dark surfaces have a low albedo and light surfaces have a high albedo.