"Meals on wheels"  is a free  service, ___  hot meals are delivered to elderly people who  

may not be able to move around very easily.  [    ]

A.that        

B.which    

C.where    

D.what

在大肠埃希菌DNA聚合酶Ⅲ中，负责校对功能的亚基是（）。

A.α

B.ε

C.β

D.δ

E.τ