答案是 d) :
It's almost four hours' drive.
例：
A visit to the Grand Hotel requires planning:mainly because it's almost four hours' drive away.
这里 four hours' 是当形容词用的.
另一个正确语法的说法是
It's almost a four-hour drive.(four 和 hour 中间要有连字符,但考题没有给你那个选择.)