It will take____ time to finish the course. A one and a half years' B.a year and a half

Question

C.one and a half year's D.a year and a half's
选哪个？要表示……的时间，就可以排除B，但是one and a half years=a year and a half，
我怎么觉得A和D都对呢？
详细、准确的解释一下

Answer 1

A,因为one and a half years' time=one year and a half,都表示“一年半的时间”追问

one and a half years也可以等于a year and a half吧

Answer 2

one and a half years'=one year and a half's追问

one and a half years也可以等于a year and a half吧

Answer 3

a追问

为什么？怎么觉得A和D都对呢？