Step 1: Recall the legal definition, a patent is a time bound exclusive right, typically lasting around 20 years from filing.
Step 2: Because the exclusivity has a fixed expiry date, any claim describing it as permanent must be false, while claims about stimulating innovation, blocking entry, and encouraging invention all match how patents actually work.
Step 3: Matching each option against this definition leaves only one contradiction.
\[\boxed{\text{Patents enable a firm to be a permanent monopoly}}\]