Tropical rainforests have been an important lofe force on Earth since the beginning of time. They help (help) to keep the air we breathe fresh and clean for millions of years. For the last fifty years, however, we have caused (cause) a lot of damage by cutting them down for industrial purposes.
Deforestation was (be) a problem since the middle of the nineteenth century, when the industrial revolution started (start). The problem grew (grow) more and more quickly since then, and for the last two decades, we reduced ( reduce) our rainforests at the rate about 100 000 squaere kilometers every year.