根据句意和汉语注释，写出单词的正确形式。
The mid-term exam will be held ________ (大约) the middle of November this year.
Did you take the ________ (药) this morning, Mary? You look ill.
The old man couldn’t remember the ________ (领导) name, but he was really grateful to him.
Hiking in Qomolangma (珠穆朗玛峰) is the ________ (费力的) walk all over the world.