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

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