Preferably, the agent is an anionic polymer comprising a chain or backbone containing repeating units each preferably containing at least one carbon atom and preferably at least one directly or indirectly pendent, monovalent delivery-enhancing group and at least one directly or indirectly pendent monovalent retention-enhancing group geminally, vicinally or less preferable otherwise bonded to atoms, preferably carbon, in the chain.
感觉挺难的 |
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