第二节．完成句子。(每空0.5分，满分10分)
1. Who _______ ________(提出) a theory about black holes ?
2. It shows that a knowledge of first aid can_______ ______ real ________(发挥重要作用).
3. You’ll find your colleagues very eager to assist you, so you may be able to______ _______ (集中)photography later if you are interested.
