题目

When we visited Hainan again ten years later, we found it changed so much that we      could hardly _______ it.    A. remember        B. think about       C. believe       D. recognize 答案：D 解析: 略如果a，b，c共面，b，c，d也共面，则下列说法正确的是A.当b与c不共线时，a，b，c，d共面B.当b与c共线时，a，b，c，d共面C.当且仅当c＝0时，a，b，c，d共面D.当b与c不共线时，a，b，c，d共面