The Nomination of a Candidate Gene Is Usually Based on All

The nomination of a candidate gene is usually based on all EXCEPT which of the following techniques?

A) a search of the literature for genes known to be involved in producing a behavior similar to the one in question
B) a comparison of the sequence of the gene to the sequences of genes in another organism
C) a systematic examination of single genes until one scores a "hit"
D) Any of the above are commonly used.