— Can you keep an eye on my bag, Tom? I
题型：选择题
问题：
— Can you keep an eye on my bag, Tom? I just want to use the bathroom.
—____. It will be safe with me.
A．Go ahead
B．I think so
C．Not at all
D．You’re welcome
题型：选择题
用下图所示的电路可以测定未知电阻Rr的阻值。已知电源电压恒定，当单刀双掷开关S接a时，电流表的示数为0.3安；当S接b时，调节电阻箱R的旋盘，直到电流表示数又为0.3安为止，读取电阻箱的电阻值为
60欧。由此可知，Rr的阻值为_____欧。
