题目

The teacher asked a very difficult question. It was Ted who finally _____ a good answer. A . came up with B . had raised C . went through with D . put up with 答案：A用显微镜观察人的口腔上皮细胞的临时装片时，在视野中有黑色圆圈，用镊子轻碰盖玻片发现圆圈可变形．则这黑色圆圈可能是（　　）A．气泡B．食物残渣C．死细胞D．未染上色的细胞