大庆原油属（）硫原油，中东原油大多是（）硫原因。
A.含，高
B.低，高
C.低，含
D.低，低
参考答案：B
The first textbooks written for teaching English as a foreign language _____ in the 16th century. [ ]
A. came about
B. came out
C. came along
D. came up
发动机正常运转，发电机（）时，对蓄电池进行充电。
A.不发电
B.电动势高于蓄电池电动势
C.电动势高于蓄电池电动势
D.过载
