And there's only two countries, the U.S. and the former Soviet Union, that had major efforts on trying to create biological warfare agents.

世界上只有美国和前苏联曾经花大力气研究生物武器。

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And there's only two countries, the U.S. and the former Soviet Union, that had major efforts on trying to create biological warfare agents.

世界上只有美国和前苏联曾经花大力气研究生物武器。

youdao