Which of the Following Properly Describes the Accounting for Goodwill

Which of the following properly describes the accounting for goodwill?

A) Goodwill is created when it is internally generated.
B) Goodwill is amortized over its useful life.
C) Goodwill is the difference between the amounts paid for a company relative to the book value of the company's net assets.
D) Goodwill is written-down when it has been determined to be impaired.