1,We are obliged to stay at home for two weeks.=>We have to... 2,It's years since i last wrote to her.=>I have not ... 3,We are going to give a (present)... about water pollution. 4,Many people have received medical (treat)... because of the disease. 5,(industry)... has caused the problem of air pollution. 6,The (reduce)... in air pollution was dramatic last year. 7,Students are taught about (environment)... issues at school. help me pls