With the pace of change quickening, more and more scientists find it hard to keep up with the latest development even in their own_____.

A．disciplines

B．majors

C．realms

D．circles

临床上能区分直肠和肛管的解剖标志是

A．直肠瓣
B．齿状线
C．直肠柱
D．肛窦
E．直肠壶腹