1. The librarian ____________ (禁止)these books to be taken out of the reading room.
2. George didn’t find it difficult at all, but it was really a ____________ (富有挑战性的) task for me.
3. There are many ____________ (争论) against smoking. Some are for it while some are against it.
4. We finished the work on time under the ____________ (指导)of an expert in the field.
