A:marking
B:marked
C:being marked
D:have been marked
物质的性质决定用途,下列物质的用途中利用其物理性质的是( )
已知X是离散型随机变量,P(X=1)= 23 ,P(X=a)= 13 ,E(X)= 43 ,则D(2X﹣1)等于( )