与尿结石形成相关的主要细菌是()
A．大肠杆菌
B．绿脓杆菌
C．变形杆菌
D．葡萄球菌
E．肠杆菌
参考答案：C
In the foreign trade business, the payment is always made by L/C. In this sentence, L/C is the abbreviation for ( ).
A．Bill of Lading
B．Commercial Invoice
C．Buying Contract
D．Letter of Credit
下列微粒中半径最小的（ ）
A．Na+
B．Al3+
C．K+
D．S2-
