肛管的括约功能主要靠（）。

A.外括约肌的深部

B.内括约肌

C.肛提肌

D.肛管直肠环

E.外括约肌的皮下部

Which of the following statements about different types of bonds is least likely correct（）

A. Municipal bonds are traded primarily on the New York Stock Exchange.

B. Tax-backed bonds are backed by the full faith and credit of the issuer’s entire taxing power.

C. Government-sponsored enterprises issue securities directly in the marketplace, but federally related institutions generally do not.