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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _assemble_conversion(stmt):
 """Assemble a Conversion statement into text."""

    reactants = _join_list([_assemble_agent_str(r) for r in stmt.obj_from])
    products = _join_list([_assemble_agent_str(r) for r in stmt.obj_to])

    if stmt.subj is not None:
        subj_str = _assemble_agent_str(stmt.subj)
        stmt_str = '%s catalyzes the conversion of %s into %s' % \
            (subj_str, reactants, products)
    else:
        stmt_str = '%s is converted into %s' % (reactants, products)
    return _make_sentence(stmt_str)