One study found that employees took an average of 7.8 days off work through sickness last year, a fall from 8.5 days the previous year.
以上是國考英文題出現的句子。
想請問知識大大們,為什麼句末的the previous year前面不用加介系詞in----in the previous year 呢?例如像in the past year前面就有介系詞in。
謝謝。: )