Strain breeding(菌种选育)(名词解释)
A.gene movement between cultivated plants and wild ones is inevitable
B.new research shows that genetically modified plants are likely to develop into weeds
C.cross-breeding is a natural process
D.hybrids are generally more successful at breeding than natural plants
What step is essential to the traditional production of flu vaccine?
[A] Manufacturers implant the vaccine into ordered chicken eggs.
[B] Scientists identify the exact strain soon after a flu pandemic starts.
[C] Public health measures are taken as an important pandemic-fighting tool.
[D] Viruses are deadened and made clean before being put into vaccine use.