In order to determine the probable function of a particular sequence of DNA in humans, what might be the most reasonable approach?

A) Prepare a knockout mouse without a copy of this sequence and examine the mouse phenotype.
B) Genetically engineer a mouse with a copy of this sequence and examine its phenotype.
C) Look for a reasonably identical sequence in another species, prepare a knockout of this sequence in that species, and look for the consequences.
D) Prepare a genetically engineered bacterial culture with the sequence inserted and assess which new protein is synthesized.
E) Mate two individuals heterozygous for the normal and mutated sequences.