Heat generated by Friction A. Caused by Electromagnetic waves
B. Caused by mixing to substances together
C. Caused by the force of two opposing motions
D. None of the above

The answer is C

Explanation:

because if you pull or push something, friction will always push or pull the opposite way

? you expect us to answer this? ? this is your schoolwork, i don't think we can with this, i think it would considering being

hydrocarbons are organic compounds that contain only hydrogens and carbons. they can be saturated (those which contain only carbon-carbon single bonds) or unsaturated (those which contain carbon-carbon double or triple bonds) in nature. hydrocarbons can undergo several reactions like substitution, elimination etc.  

on substituting one or more hydrogen atoms in hydrocarbon it results in the formation of haloalkane. as the halogen atoms are large compared to the carbon and hydrogen atoms, due to which the molecular weight increases and the bond become polar because of presence electronegative halogen atom and results in the increase in boiling point of the haloalkane.

thus, the correct option is (b) that is the boiling point of the new compound increases on substituting a hydrogen atom with a halogen in a hydrocarbon.