⑴____A. sixteen B. seventeen C. apple
⑵____A. thirteen B. nineteen C. nine
⑶____A. twenty B. five C. fourteen
⑷____A. eighteen B. crayon C. fruit
⑸____A.eleven B. twelve C. thirteen
把弯曲的河道改直,能够缩短航程,这样做的道理是( )