Put the verbs in brackets into the correct passive form.
1) Global warming is called (to call) the greenhouse effect because the gases above the earth make the planet comparable to a greenhouse.
2) The term «acid rain» refers to what scientists call «acid deposition». It_______(to cause) by destructive airborne acidic pollutants.
3) Acid rain________(to discover) in 1852, when the English chemist Robert Agnus invented the term.
4) Recently, a more intensive research on the true causes of acid rain________(to do) so that countries have the information they need to prevent acid rain and its dangerous effects.
5) Air pollution can__________(to find) both outdoors and indoors.
6) Every year, 14 billion pounds of sewage, sludge, and garbage__________(to dump) into the world’s oceans.