如何提高氩提取率？
参考答案：
①保证主塔精馏工况稳定
②降低氩馏分中的含氧量
③降低氩馏分中的含氮量
④防止氮塞
--- She's never spoken to a foreigner, _______?
--- Yes. She is active and can speak English freely.
A． is she
B．has she
C．isn't she
D．hasn't she
稻曲病发生主要与下列哪些气候关系最密切（）
A、温度
B、湿度
C、光照
