—What do cows eat?
—They eat_______ grass.[ ]
A. most
B. mostly
C. almost
D. main
答案:B
设{an}为等差数列,Sn为其前n项和,且a3+a5=4,则S7等于( )
A.13
B.14
C.15
D.16
晶闸管控制电抗器和晶闸管投切电容器组合型静止无功补偿器SVC如何构成?有何特点?