求教GWD-12-Q14:

GWD-12-Q14:

In 1914 a total of 469,000 cars and trucks were produced
in the United States,
but in 1929 almost twice the numbers of tucks alone came off the
assembly lines.

A.     
the numbers of tucks alone

B.      
that number of trucks alone

C.     
the number of trucks by themselves

D.     
as many trucks themselves

E.      
as many trucks by themselves

答案是B， 问个弱弱的问题， 为什么number可以came off the assembly lines呢?