Great changes ___ in the city, and a lot of factories ___.

A．have been taken place, have been set up

B．have taken place, have been set up

C．have taken place, have set up

D．were taken place, were set up

用铜锌合金制成的假金元宝欺骗行人的事件屡有发生。下列不易区别其真伪的方法是[ ]

A．测定密度

B．放入硝酸中

C．放入盐酸中

D．观察外观