下列几种细胞结构中，不属于生物膜系统的是[ ]
A．
B．
C．
D．
答案：B
---Where did you first meet your boyfriend?
---It was in the department store ______ he worked.
A．which
B．that
C．what
D．where
当脉冲宽度为1μs时，它们每个脉冲的空间长度为（）M。
