Answer: a)Purchased from a vendor and gives you the right to use the software but is not yours to own.
Explanation: Proprietary software is the software that can be used by the user but it has copyright of the vendor/holder in any case.There are some certain condition under which the user can use this software.The distribution of the software is not permitted in this case. No modification or manipulation can be done by the user.
Other options are incorrect because it is not free as its purchased from vendor ,not freely available rather guided by owner and can be used over certain period of time.Thus , the correct option is option(a).