76. Young people of different nationalities
77. There are ten expeditions every year.
78. ten weeks (trong câu: Each expedition lasts for ten weeks and takes 150 volunteers. )
79. The volunteers do environmental research. (trong câu: Others work in national parks or help scientists to do environmental research. - cuối đoạn 2)
80. English (trong câu: To become a volunteer, you have to be between
you have to speak some English and you also have to be enthusiastic, flexible and hard-working members of a team. - câu cuối cùng của đoạn.)
