道岔由反位向定位转换时,反位启动电路要经过分线盘的()和()端子。()
A: X1、X3
B: X1、X4
C: X2、X3
D: X2、X4
A: X1、X3
B: X1、X4
C: X2、X3
D: X2、X4
举一反三
- 继续上题，为了程序编写简洁，要给数据框x中的6列重新命名为x1,x2,x3,x4,x5,x6,应该使用的命令是（） A: ColNames(x) <- c("x1","x2","x3","x4","x5","x6") B: Names(x) <- c("x1","x2","x3","x4","x5","x6") C: colnames(x) <- c("x1","x2","x3","x4","x5","x6") D: colname(x) <- c("x1","x2","x3","x4","x5","x6")
- 以下程序片段的运行结果是_________。 int x1=30,x2=40; sub(int x,int y) { x1=x; x=y; y=x1; } int main() { int x3=10,x4=20; sub(x3,x4); sub(x2,x1); printf(“%d,%d,%d,%d\n”,x3,x4,x1,x2); }
- 设总体X服从均值为1/2的指数分布,X1,X2,X3,X4为来自X的样本,则X1,X2,X3,X4的联合概率密度为A.()正确B.()错误
- 设总体X服从均值为1/2的指数分布, X1, X2, X3, X4为来自X的样本, 则X1, X2, X3, X4的联合概率密度为[img=445x103]180387e18db7cd2.png[/img]
- 设总体X～N(μ，σ2)，x1，x2，x3，x4为来自总体X的样本，且