对经济增长源泉的研究依赖于( )。
A．增长抵消 B．增长核算 C．增长估算 D．增长持平
参考答案：B
平行光线经过某镜片后在2m处形成焦点，该镜片的屈光力为（）
A.2D
B.1D
C.3D
D.0.5D
E.0.25D
One of the very important documents in the foreign trade business is BL. B/L is the abbreviation for ______.
A．Bill of Lading
B．Commercial Invoice
C．Buying Contract
D．Letter of Credit
