I.根据本单元所学单词及所给的提示，写出所缺单词的正确形式。
1. It is difficult to p________ what the long-term effects of the accident will be.
2. It is e________ that Jenny is happy, for she is smiling.
3. They have no children of their own, but they’re hoping to a________ one.
4. We may talk of beautiful things, but beauty itself is ________ (抽象的).
