Question 1:What are the three classes of macromolecules taken as food energy by humans?

for question 1:
lipids, proteins and carbohydrates are consumed as food energy. (the 4th type is nucleic acids which u cant consume).

for question 2:
well, in the process of digestion, food is broken down into simpler substances. synthesis and hydrolysis dont break down food (well, these proceses actually combine them). in the process of dehydration, the food loses water molecules and becomes dry.

so if i consider the choices that u have given then only dehydration could be important.

1.  Carbohydrates, lipids, and proteins.
2.  If you're talking about what goes on in the digestive system, the answer is hydrolysis.  It is used to break carbohydrates and proteins down into their components (sugars and amino acids, respectively).  Don't ask me about lipids, LOL, because I don't know;  I rather expect that they also undergo hydrolysis to release the "fatty acids."  The monomers are what's absorbed by the cells lining the digestive tract.  (A lot of other crud is also absorbed, and subsequently detoxified by the liver and/or removed by the kidneys).

well, go flipped some biochemistry book on introduction to metabolism u will know both process is important.

1. protein, fats and glucose. (non-essential, nucleic acid)
2.most of the time only hydrolysis happened in ur stomach and small intestine and few enzymes will play their roles. food will be broken down into small fundamental particles to transport across the endothelium cells of small intestine and stomach. when those small particles are transport to liver metabolism happened inside it. fats will be broken down into glycerols and fatty acid, but fatty acid will be further catabolysed to acethyl CoA y 4 consequence reaction include dehydration and hydrolysis. both protein and glucose will undergo hydrolysis and dehydration and many more processes. for protein aminotransferation is important in the sense of building up essential amino acid. Glucose mostly undergo phosphorylation and isomerization in glycolysis and gluconeogenesis. i wont be able to talk in details as it would take a few more thousand words.
Go read some books for more details.

Cheers!

1.carbohydrates,proteins and fats.
2.hydrolysis as all the digestion processes are hydrolytic enzymatic processes, i.e.they use water molecules in conjunction with energy in the form of ATP to break down the complex food ingested into simpler forms, eg. carbohydrates into dissacharides and monosaccharides by amylase(pancreatic enzyme)