Every few years, the coal workers ______their lungs X-rayed to ensure their health.A.
Every few years, the coal workers ______ their lungs X-rayed to ensure their health.
A. are having
B. have
C. have had
D. had had
根据时间状语every few years,可判断本句应为一般现在时,因此答案选B。
f(x)=e^2x-1f''(0)=?f'(x)=2e^2x–1f''(x)f(x)=e^2x-1f 数学 2020-03-30 …
用洛必达法则求一个函数的极限lim(x→∞) [(e^x-e^(-x)/(e^x+e^(-x)] 数学 2020-05-16 …
已知f(x)=e^x-e^﹣x,g(x)=e^x+e^﹣x(e=2.718…).设f(x)·f(y 其他 2020-05-16 …
定义在R上的偶函数f(x-2),当x>-2时,f(x)=ex+1-2(e为自然对数的底数),若存在 其他 2020-05-23 …
协方差等于零能推出相互独立吗?∵cov(X,Y)=0又∵cov(X,Y)=E(XY)-E(X协方差 其他 2020-06-10 …
如图所示,在平行六面体ABCD-A1B1C1D1中,点E为上底面对角线A1C1的中点,若=+x+y 数学 2020-07-12 …
薛定谔方程:-(h^2/2m)(d^2/dx^2)§(x)=E§(x)、用§=exp[ax],代入 数学 2020-07-21 …
(1+x)e∧-x的导数是多少(1+x)e^(-x)的导数是多少请各位大大帮帮小弟 数学 2020-07-23 …
函数f(x)=ex-x(e为自然对数的底数)在区间[-1,1]上的最大值是()A.1+B.1C.e 数学 2020-08-02 …
已知函数f(x)=(x2-3x+9/4)e的x次方,其中e是自然对数的底数.已知函数f(x)=(x 数学 2020-08-02 …