Selected Graduates's examination questions are arranged with a pair of scissors, a pair of tweezers, a writing brush, a bowl of paste and a desk lamp.

A pair of scissors, a pair of tweezers, a writing brush, a bowl of paste, a desk lamp ... In the ancient books center of the library, ancient book restorers repeat their work year after year. Faced with precious ancient books that need to be restored, they are always _ _ _ _ _.

The most suitable items to fill in the underlined part are:

A. Be unsmiling

B. Walking on thin ice

C. Excellent

D. treat it as a treasure

The first step of analysis is to analyze the context. According to the "restored precious ancient books", the meaning of this article is caution.

The second step is to identify the options. A "unsmiling" describes a serious attitude; Item c "strive for perfection" means to strive for better after doing it well; Item d "regard it as a treasure" describes it as very precious and regards it as priceless. Items A, C and D do not mean "be careful" and are out of context, so they are excluded. The metaphor of "walking on thin ice" in item B is extremely cautious and wary, which is in line with the meaning of the text.

Therefore, choose option B.