vaccines(疫苗)arecomplexbiologicproducts.      strongman...

问题详情：

 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

【回答】

A

知识点：非谓语动词

题型：选择题