1.   But human embryos must be destroyed to obtain these stem cells.

2.   But in most cases a human embryo must be destroyed to obtain them.

3.   But opponents, including anti-abortion groups, oppose certain types of stem-cell research because of their belief that a human life was destroyed to obtain the cell.

4.   Levy said that in order to test an animal for rabies, it must be destroyed to obtain tissue from its brain stem for testing.

5.   The president opposes even research cloning because it involves the creation of embryos that are then destroyed to obtain stem cells for research and potential treatments.

6.   The process is controversial because human embryos must be destroyed to obtain stem cells, which are created in the first days of pregnancy and grow into human bodies.