F质粒的IS元件使F质粒与大肠杆菌染色体之间发生同源重组，产生一个（）细菌。
参考答案：Hfr
两圆的半径分别是3cm和1cm，圆心距为4cm，则两圆的位置关系是______．
I don’t really like the author,_______ I have to admit his books are very exciting.
A．although
B．unless
C．until
D．once
