GMAT Sentence Correction (SC) | Omission while Comparing

I)
INCORRECT: Prices at the producer level are only 1.3 percent higher now than a year ago.
CORRECT: Prices at the the producer level are only 1.3 percent higher now than those of a year ago.

2)CORRECT: Wild animal have less total fat than livestock.
CORRECT: Wild animal have less total fat than that of livestock.

3) CORRECT: Heating oil prices are expected to be higher this year than last
CORRECT: Heating oil prices are expected to be higher this year than those of last.

Here why is the first
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