积液的声像图特征性表现为（）①有清晰易辨的边缘②具有良好的声传导③无回声④含有相当多的碎片
A.①③④
B.②③④
C.①②③
D.①②③④
参考答案：C
如图有关下列食物网的叙述，正确的是
A．该食物网有3条食物链
B．鹰与鸟的关系是既捕食又竞争
C．该食物网所处的生态系统为草原生态系统
D．鹰占有两个营养级
When the foreign guest arrived, I found him speaking good Chinese. I _______ his speech into
Chinese the night before. [ ]
A. needn't translate
B. didn't need to translate
C. needn't have translated
D. didn't need translating
