Which of the following is a general problem associated with external credit enhancements External credit enhancements:（）

A. only provide protection against systematic risk, not against idiosyncratic risk.

B. are very long-term agreements and are therefore relatively expensive.

C. are subject to the credit risk of the third-party guarantor.

三乙基铝钢瓶和工艺管线之间采用（）连接。

A、挠性管连接

B、硬连接

C、快速连接

D、软管连接