人工脱敏是把已知变应原采取小剂量、短间隔、（）的方法，注入皮下、肌肉或口服
参考答案：连续多次
—Hi，Jim. I_______ you for a long time.
—I_______ in Beijing for two months. I’ve just comeback. [ ]
A. didn’t see; have been
B. haven’t seen; was
C. didn’t see; was
D. haven’t seen; have been
生水经过钠离子交换处理后，除去水中硬度，这种水称为二级除盐水。
