How to be Strong in accounting theory?

Dear Friends,
 I would like to be strong in accounting theory subject.  Could anyone please provide accounting questions with the one line answer?
 Example:
What is deferred revenue expenditure (DRE)?
"The benefit of which will be available in the subsequent years is called DRE.  Ex:Advertisment exp."
 Some intresting interview questions also i faced:
1.) why the balance sheet always tally?
2.)Difference between Revenue exp and deferred rev exp?
3.)why depreciation is to be provided? is it compulsory? If not provided, what will happen?
4.)
 Like the above...
  Can anyone help me?

1.The balancesheet always tallies because it is nothing but the summary of matching debit and credit entries

2. Revenue expenditure pertain to that year's while Deferred revenue expenditure pertain to following years incurred now in advance

3. Depreciation is nothing but the expenditure you have already incurred to create an asset, whose services are available over its life time extending to more than a year therefore  will have to be acoounted accordingly over its entire life time