单选题 A number of students in this class ______ to Beijing once or twice.
A. were B. have been C. is D. has been

【正确答案】 B
【答案解析】[解析] 这个班里的许多学生都去过北京一两次了。
[考点] 主谓一致及谓语动词的时态
[解析] a number of意为“许多”，后接复数名词，这时谓语要用复数。另根据句意可知，学生们已经去过一两次了，要用现在完成时。故选B。