在使用Keil STM32进行构建时，未定义的符号SystemInit(从startup_stm32f2xx.o引用)。

I am using STM32F207VC controller. and I am using uvision4 IDE, When I try to compile a simple code, I get the error tst1.axf: Error: L6218E: Undefined symbol SystemInit (referred from startup_stm32f2xx.o). . I have place stm32f2x file to my project directory.I am using STM32F207VC controller. and I am usi