原文：Obama also called climate change and nuclear proliferation "c

原文：Obama also called climate change and nuclear proliferation "challenges that neither of our nations can solve by acting alone."
译文：奥巴马也把气候变化和核扩散称为“我们两国都无法单独应对的挑战”。
【正确答案】：
改译：奥巴马也把气候变化和核扩散称为“我们两国都无法单方面应对的挑战”。