历史研究在确定课题之前的首要工作()。
A、收集史料
B、实证研究
C、田野调查
D、史的研究
参考答案:D
He is the only person who saw the accident ______. So he is the most important witness.[ ]
A. happen
B. to happen
C. having happened
D. happened
近地面风向是( )
A.垂直于等压线并指向高压
B.垂直于等压线并指向低压
C.与等压线平行
D.指向低压并与等压线斜交