Under 37 CFR 11.108, a practitioner must not acquire a proprietary interest in the cause of action being litigated. However, which of the following interests IS permitted?
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A
A contingent fee in a civil case as permitted by the rules
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B
Ownership of the patent being prosecuted on behalf of the client
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C
A lien on the client's invention for unpaid fees exceeding 25% of the patent's value
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D
An assignment of patent rights as full payment for prosecution services