in 1914 a total of 46900 cars and trucks were produced in US,but in 1929 almost twice (the numbers of trucks alone) came off the assembly lines.()部分是划线部分 B that number of trucks alone C the number of trucks by themselves 答案选B,C为什么不对呢?我觉得C读起来怪怪的。。有点疑惑。。