下面的短文有15处空白，请根据短文内容为每处空白确定一个最佳选项。
One Good Reason to Let Smallpox Live
It's now a fair bet that we will never see the total extinction (灭绝) of the smallpox (天花) virus. When smallpox was completely got rid of in the world, scientists wanted to (51) the killer virus in the last two labs - one in the US and one in Russia. They asked: If smallpox has truly gone from the planet, (52) point was therein keeping these reserves？
in reality, of course, it was naive to (53) that everyone would let go of such a powerful potential weapon.Undoubtedly several nations still have (54) vials (小药瓶). And the last "official" stocks of live virus bred mistrust of the US and Russia, (55) no obvious gain.
Now American researchers have (56) an animal model of the human disease, opening the (57) for tests on new treatments and vaccines (疫苗). So once again there's a good reason to (58) the virus -just in (59) the disease puts in a reappearance.
How do we (60) with the mistrust of the US and Russia？ (61) . Keep the virus (62) international support in a well-guarded UN laboratory that's open to all countries. The US will object, of course, just as it (63) a multilateral (多边的) approach to just about everything. But it doesn't mean the idea is (64) . If the virus is useful, then let's (65) it the servant of all humanity - not just a part of it.
51 A destroy B improve C change D transport