在一个农田生态系统中,若含有DDT,经过一段时间,以下生物体内的DDT浓度最高的是 [ ]
A.禾谷类
B.昆虫
C.食虫鸟
D.鹰
答案:D
By the end of 1989 many buildings _____ built in the city.[ ]
A. will
B. have been
C. had been
D. have
表示惊讶、怀疑、讽刺等感情的句子多用()
A、升调
B、降调
C、曲调
D、平调