运用使用年限法评估设备成新率时，一般首选（）作为设备的总使用年限。
A.自然寿命
B.经济寿命
C.技术寿命
D.折旧寿命
参考答案：B
再生性钠泵
He worked hard, ____ a skilled doctor. [ ]
A. aimed at becoming
B. aiming in becoming
C. aiming becoming
D. aiming to become
