Most of the country's biggest daily newspaper had lower circulation in the six months from October 1995 through March 1996 than a similar period a year.
(A) a similar period
(B) a similar period's
(C) in a similar period
(D) that in a similar period
(E) that of a similar period
这题的答案是C,我选的E,想知道为什么选C.
我认为是1995年10月到1996年3月这6个月的circulation 和 之前一年同时期的circulation进行比较,所以要用that of 指代 criculation。