A:he returned, did he know
B:he returned, he knew
C:did he return, did he know
D:did he return, he knew
分解因式:2x2﹣8y2=____.
研究发现两种现象:①动物体内的B细胞受到抗原刺激后,在物质甲的作用下,可增殖、分化为效应B细胞;②给动物注射从某种细菌获得的物质乙后,此动物对这种细菌具有了免疫能力。则这两种物质中( )