... children. ( strict) IV- Choose the best answer: 1.What should you do to (keep - protect - prevent - reduce) the environment? 2.(Forest - Forestry - Deforestation - Forests) .is one of the causes of flood. ... must be (heavily- heavy - heavily) fined. 6.If we (pollute – polluting – pollution - polluted) the water, a lot of fish will die. 7.He is tired (Therefore - because - however - so) he has to ... V- ing. S + AM/ IS/ ARE + NOT + V- ing. AM/ IS/ ARE + S + V- ing? Now = at present = at the moment: bây giờ Past simple S + WAS/ WERE + V- ing. S + WASN’T/ WEREN’T + V- ing. WAS/ WERE + S + V-ing?...