The primary difference among them is how long their effects last.

The primary difference between the two engines was the stroke.

The primary difference between the games is how signals operate.

The primary difference between the two concepts concerns the status of the subject.

The primary difference was whether leaders accepted the value of negative thinking or not.

Perhaps the primary difference between this year and last is that Dave finally did do something.

That, he concluded, was the primary difference between the two.

The primary difference is the time required to achieve them.

There are several major differences between the two breeds, with the primary difference being the size.

The primary difference between free software and open source is one of philosophy.