一、单项选择题
1、 vaccines (疫苗) are complex biologic products. strong management and if not correctly, vaccines can lose same of their effectiveness.
A. requiring; handled B. requiring; handling
C. required; handling D. required; handled
2、In art criticism, you must assume the artist has a secret message _________ within the work.
A.to hide B.hidden C.hiding D.being hidden
