①钢铁 ②机械 ③石油 ④电子 ⑤食品 ⑥服装
A:① ② ③
B:② ③ ④
C:③ ④ ⑤
D:④ ⑤ ⑥
若等差数列{an}满足a12+a102=10,则S=a10+a11+…+a19的最大值为( )
方程x2=4x的解是( )。
The doctor recommended that I________here for sunshine to help me to get over my illness.