Plane为可数名词单数,不能单独放在句中,应在其前加冠词或把它变为复数,而本句后有a machine, 因此只能在其前面加a,变为A plane。 9. He played a piano at the party yesterday. 把a 改为the ,因为乐器前用定冠词。 10. The machine was invented in 1920s. 在in后加t...