Stem cells are cells that can self-renew and differentiate into specialised cell types. Because of their potential to replace diseased or defective human tissue, stem cells are seen by scientists as key to developing new therapies for a wide range of conditions, including degenerative illnesses and genetic diseases. Treatments based on adult stem cells - from sources such as umbilical cord blood - have been successfully developed, but what makes stem cell research controversial is the use of embryonic stem cells. Not only do embryonic stem cells reproduce more quickly than adult stem cells, they also have wider differentiation potential. The main opponents to stem cell research are pro-life supporters, who believe that human life should not be destroyed for science. Advocates of stem cell research counter this crucial point by saying that an embryo cannot be viewed as a human life, and that medical advances justify the destruction of embryos. Furthermore, stem cell research utilises the thousands of surplus embryos created for in vitro fertilisation treatment. The issue is particularly divisive in the United States, where federal funding is not available for the creation of new embryonic stem cell lines, although recent legislation has opened up government funding to further research on embryonic stem cells created through private funding. Whereas many governments prohibit the production of embryonic stem cells, it is allowed in countries including the UK, Sweden and the Netherlands.

Question: Stem cells are at the forefront of medical research because of their ability to grow indefinitely.
Options:
A. true, B. false, C. uncertain
Answer: "C"