用动词的正确时态填空
Ourdesksandchairs________________(make)ofwood.Thepaperofbooksandnewspapers______also___________(make)fromwood.Evensomekindsofcloth__________________(make)fromit.Manypeople____________(burn)woodtokeepthemselveswarminwinter.Indeed,wood_______(be)importantinoureverydaylife.
Where________wood__________(come)from?It________________(take)fromtreeswhich_____________(grow)inthemountains._________you____________(know)howit____________(get)tousfromthemountains?
Firstofall,trees___________(cut)downwhenthey______________(grow)bigenough.Thentheirbranches_______________(cut)off,andlogs_______________(make).Theseheavylogs________________(put)togetherindifferentwaysand_________________(take)downtothefootofthemountains.Someofthem_________________(float使漂流)downthesmallriversandothers_________________(carry)downontrains.
Bigtrees________________(cut)downinthemountainseveryyear.Thenyoungones______________________(must,plant)sothatwe______always________________(can,have)enoughwood.Wehavetotakegoodcareofmountainssothatthey__________always_________________(may,cover)withgrowingtrees.