They are experienced porter(搬运工)who know how to the weight of the rocks they carry.
73. It is not right _____ a person who is _____ trouble.
72. We couldn’t read the notice on the board because several people were standing _______ it.
71. People eat a lot of sugar __________ cakes, soft drinks, sweets and so on every day.
70. I know it is difficult __________ him to talk like the lecturer, but I think he should grasp every chance .
69. With the guide leading the way, the visitors were able to travel through the forest not by air but _____ foot.