When asked about their opinions about the schoolmaster, many teachers would prefer to see him step aside ________ younger men.(2011·湖北，30)

A．in terms of

B．in need of

C．in favor of

D．in praise of

脊椎动物亚门除了脊索、背神经管、鳃裂基本特征外，还有哪些进步性特征？