What Has Affected the Preliminary Results from Some Recently Initiated

What has affected the preliminary results from some recently initiated gene therapy trials?

A) The laboratories have not had enough time to develop a gene-therapy protocol.
B) Congress is hesitant to fund any more experimental programs at the National Institutes of Health.
C) Cells into which corrected genes are introduced cannot find and copy these genes to make new proteins.
D) There is a voluntary moratorium on gene therapy research because of the fear of introducing a toxic gene into the environment.
E) Drug companies are stalling the research projects until they can get assurances about development patents.