第27题: [单项选择]The last half of the nineteenth century ______ the steady improvement in the means of travel. A. has witnessed B. was witnessed C. witnessed D. is witnessed 参考答案:C 答案解析:[解析] 句中空格后有宾语,可先排除表示被动的B、D两项。A、C两项的区别在于时态。根据主语the last half of the nineteenth century(19世纪后半叶)应选择过去时