1过去式：could
过去式题目：
1. You originally _could_(can) go yesterday. 昨天你本来可以去。
2. It _could_(can) be different yesterday from today. 今天和昨天会有很大的不同。
3. They _could_(can) have left yesterday, but they didn't. 他们本来可以昨天走，但是没走成。
4. If it had not rained yesterday we _could_(can) have played tennis. 如果昨天没有下雨的话我们就可以打网球了。
5. She _could_(can) have told Jim yesterday about the delay of the party. 她昨天可能告诉吉姆晚会推迟的事了。
2过去分词：could
过去分词题目：
1. Yet, if we look more closely, we'll see that even the little we have _could_(can) be shared with others. 但只要仔细的观察一下，我们就会发现，即使我们拥有得很少，也总有可与人共享的。
2. Conventional report of geotechnical investigation have _could_(can) not satisfy our requirement about space analyse. 传统的岩土工程勘察报告越来越不能满足人们空间分析的需求。
3. Before the librarian could even start her speech he said, scornfully, "That other librarian we had _could_(can) write." 图书管理员还没来得及说话，这个男孩就挖苦道：“我们以前的那个图书管理员会写字。”
