痈切开引流时正确的切口是（）。

A.两条横切口

B.两条纵切口

C."+"或"++"形切口

D."上"形切口

E."T"形切口

One theory, ________ suggested by Harvard University, is that humans began cooking their food, thereby releasing nutrients locked in the raw food and reducing the time needed to chew it.

A．which

B．as

C．that

D．what