根据句意和汉语注释，写出单词的正确形式。

小题1:The mid-term exam will be held ________ (大约) the middle of November this year.

小题2:Did you take the ________ (药) this morning, Mary? You look ill.

小题3:The old man couldn’t remember the ________ (领导) name, but he was really grateful to him.

小题4:Hiking in Qomolangma (珠穆朗玛峰) is the ________ (费力的) walk all over the world.

QS1型交流电桥是采用“平衡比较”原理，当被试设备接入测试电路后，调整输入和输出桥臂的电压、电流乃至阻抗达到平衡，使电桥中检流计G的电流Ig=0。这时，可调电容C4的值就等于被试设备的介质损耗正切值。