+0
Hello,

a. It is a two hour drive from [Place A] to [Place B].
b. It is a two hour's drive from [Place A] to [Place B].
c. It is a two-hour drive from [Place A] to [Place B].

Which is/are correct use?

I believe that (c) is of course right.

According to Longman Dictionary of Contemporary English (LDOCE), in the entry of "drive ," (a) is used. I believe that (a) is right as well.

However, why is the hyphen in the compound adjective dropped sometimes.
With the hyphen dropped, it seems no longer compound and adjectival.

In LDOCE, in the entry of drive, "" is given as a phrase.
I wonder whether 's is used after hour only when the number is one/an?

Regards
+0
.
The hyphen or lack of same is of no consequence in A and C. The hyphen is required if confusion ensues without it. I would be more interested in seeing a hyphen in B to avoid the perceived paradox of 'a two'. The possessive is possible with plural units, I think.
.
+0
exodejavua. It is a two hour drive from [Place A] to [Place B].
b. It is a two hour's drive from [Place A] to [Place B].
c. It is a two-hour drive from [Place A] to [Place B].
C. is the best alternative. A. is fine with me but some may object to the lack of a hyphen. As Mr M has said, the sentence is intelligible without a hyphen and many people do leave it out. B. is badly wrong because you need the plural genitive if there are two hours. Two is more than one. It is possible to use the genitive, and if you do, the article is optional: It's [a] two hours' drive... A goes with drive and in English the genitive is such a "strong" grammatical structure that an indefinite article is rarely used before a noun in the genitive to refer to another noun that follows it. (I hope you understand what I mean!Emotion: smile)
CB
Students: Are you brave enough to let our tutors analyse your pronunciation?
Comments  
a two-hour drive!! or "two hours' drive"
Students: We have free audio pronunciation exercises.