苏联高度集中，高度封闭的报业体制特点是：（），报刊管理高度集权，（），信息来源十分单一，（）。
参考答案：报刊媒介全部国有；报刊功能只重宣传；报刊言论高度统一
食物中毒的产生原因是食物本身含有有毒物质。（）
— Li Na went out of the China Open in the first round. Why should she be defeated by such
an unknown player?
— Well, that's OK. She __________ enough after becoming the world champion. [ ]
A. could not train
B. must not have trained
C. can not train
D. may not have trained
