The right answers are B, C and D.
An enzyme is a protein with catalytic properties. Virtually all biomolecules capable of catalyzing chemical reactions in cells are enzymes; some catalytic biomolecules, however, consist of RNA and are therefore distinct enzymes: they are ribozymes.
An enzyme acts by lowering the activation energy of a chemical reaction, which increases the rate of reaction.
Convection is the transfer of energy by movement of a medium, whereas radiation is the transfer of energy by, well, thermal radiation. Conduction also requires a medium, but, again, it is a fundamentally different mechanism than either convection or radiation; in this case it is the transfer of energy through a medium.
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