药物的剂量效应曲线为
A．不对称的S型曲线
B．对称的S型曲线
C．不对称的折线
D．对称的折线
E．不规则型曲线
参考答案：B
铅锡合金熔断丝规格（铅75%，锡25%）的直径分为（）类。
A.8
B.10
C.12
D.14
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 InvoiceC．buying Contract D．letter of Credit
