a jam doughnut的用法和样例：
- Because I lost my money I was in a jam.
- I'm in a bit of a jam; can you lend me ten pounds until tomorrow?
- A jam made of fruits stewed in sugar.
- " He didn't know that in German he was saying, "I'm a jam doughnut" (in Frankfurt he would not have said that he was a Frankfurter).He could also have been laying claim to being a newspaper size.