：B单选题以下函数定义正确的是()Adoublefun(intx，inty){z=x+y;returnz;}Bdoublefun(intx，y){intz;returnz;}Cfun(x，y){doublez;z=x+y;returnz;}Ddoublefun(intx，inty){intx，y;doublez;returnz;}我的