Which of the following is true about the impairment of goodwill subsequent to the acquisition of the subsidiary?

a$.$ Testing for the impairment of goodwill has to be performed at least once a year.

b$.$ The parent's share of the goodwill impairment loss can be recorded either in the consolidation worksheet or in the parent's books.

c$.$ Both of these statements are true.

d$.$ None of these statements is true.