OG SC比较级请教

bifuyuyu

OG SC的758和784为什么比较级用的似乎有点不一样？
758 - Prices at the producer level are only 1.3 percent higher now than (those of a year ago) and are going down, even though floods in the Midwest and drought in the South are hurting crops and therefore raising corn and
soybean prices.
784 - Most of the country's biggest daily newspapers had lower circulation in the six months from October 1995 through March 1996 than (in a similar period) a year
earlier.

以上均是正确参考答案，但是两个比较级一个有those of，另一个是纯时间状语进行的比较，谁能帮忙解读一下吗？
谢谢！

SuperboyJim

引用Ron神的一句话 "for this exam, learning to WRITE comparison sentences is a complete waste of your time."


另外这里可能有你要找的答案
https://www.manhattanprep.com/gmat/forums/ron-s-advice-on-comparison-and-omission-t31036.html