请教og 81

In 1973 mortagage payments represented twenty-one percent of an average thirty-year-old male's income; and forty-four percent in 1984.

(B) income; in 1984 the figure was forty-four percent

(C)income, and in 1984 fourty-four percent

答案（B）是猜对了，但是（C）错在什么地方呢？og说是To estanlish the cleares comparison between circumstances in  1973 and those in 1984, a separate clause is needed to describe each year.难道(C)只是错在不是单独的句子？如果把（C）看成是省略表达，（C）有什么错误吗？

谢谢