刀具补偿的作用是把（）轨迹转换成刀具中心轨迹。
参考答案：零件轮廓
This famous tower has a long history. It ______ more than 300 years ago.
A．builds
B．built
C．is built
D．was built
商业承兑汇票既可以由付款人签发，也可以由收款人签发，一但银行承兑汇票只能由付款人签发。( )
