六. 短文改错（10分）
They were marching towards a building then               81._____________
they suddenly realized what the officer hadn’t left            82. _____________
him enough time to give the order to turn round              83. _____________
and to stop. So they went on marching straight               84. _____________
into the wall. The soldiers smiled happy as each of            85. _____________
those in the front line decide at the same time to walk          86. _____________
ahead. There was loud noise as they hit the wall              87. _____________
one after another. But before any of them had                88. _____________
no time to smile again, the officer shouted, “If you            89. _____________
have been in a really straight line, I could have heard          90. _____________
only one sound when you hit the wall!”