My friends who own motorcycles/a motorcycle are adventurous.

[azz]

a. My friends who own motorcycles are adventurous. .
Could I use that sentence if all of my motor-cycle-owning friends have one motorcycle each?


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b. My friends who own a motorcycle are adventurous..
Could I use that sentence if all of my motor-cycle-owning friends have more than one motorcycle each?
Could I use that sentence if some of my motor-cycle-owning friends have more than one motorcycle each?

 

[Barque]

Yes.

 

[Tarheel]

"My friends who own motorcycles" does not indicate how many motorcycles each one owns. (It doesn't have to be more than one for each individual.)