Look! He is in the river. [ ]
A. swiming
B. swim
C. swims
D. swimming
答案：D
绝对感受性与绝对感觉阈限成______关系。
一种B淋巴细胞功能缺陷的动物是（）
A.BALB／c－nu
B.CBA/N－xid
C.BALBC／c－scid
D.C57BL／6-bg
