Which of the Following Is True of Dominant Loss-Of-Function Mutations

Which of the following is true of dominant loss-of-function mutations?

A) The mutant phenotype is seen even if an additional functional copy of a gene is present
B) The mutation is present in trans but not in cis
C) The mutant phenotype is seen only in haploids
D) The mutant phenotype is seen only when two defective copies of a gene are present