防突工是负责煤矿防突措施现场实施的把关和指导、防突措施落实的督促检查、测定防突参数等工作。
参考答案:对
现要求用下列器材测量一节干电池的电动势.
A、干电池E:电动势约1.5V,内阻未知;
B、电流表mA:量程5mA,内阻为20~30Ω;
C、阻值为200Ω的定值电阻一个;
D、阻值为400Ω的定值电阻一个;
E、开关两个,导线若干.
①某同学设计了图甲所示的电路,在该电路中R应选择阻值为______Ω的定值电阻.
②请在图乙中按图甲的电路图完成实物连接.
③该同学在实验中,闭合开关S1、S2时,电流表的示数为I1;闭合开关S1、断开开关S2时,电流表的示数为I2.请写出用已知量和测得量表示的待测干电池的电动势E=______.
----I _____this morning, but he could not come.
----Well, we’d better go and _____at his office.
A.called him; call on him
B.called on him; call him
C.called at him; call
D.called him; call at him