请把下面划线部分翻译成中文。 In international business the importer may send an enquiry to an exporter, inviting a quotation and /or an offer for the goods he wishes to buy , or simply asking for some general information about these goods .
【简答题】、对于任意两个实数对( a , b )和( c , d ),规定:当且仅当 a = c 且 b = d 时,( a , b )=( c , d ).定义运算“ ”:( a , b ) ( c , d )=( ac - bd , a d + bc ).若(1,2) ( p , q )=(5,0),则 p = , q = .
【单选题】对于数对( a , b )、( c , d ),定义:当且仅当 a = c 且 b = d 时,( a , b )=( c , d );并定义其运算如下:( a , b )※( c , d )=( ac - bd , ad + bc ),如(1,2)※(3,4)=(1×3-2×4,1×4+2×3)=(-3,10)。若( x , y )※(1,-1)=(1,3),则 x y 的值是( )