—Karl Marx was born in Germany and German was his native language.

—________, as far as I know. [ ]

A. So was Engels

B. It was the same with Engels

C. So Engels was

D. Neither was Engels

某施工企业于2002年承建单位办公楼，2003年4月竣工验收合格并交付使用。2008年 5月，施工企业致函该单位，说明屋面防水保修期满及以后使用维护的注意事项。此事体现了合同法的( )原则。

A．公平

B．自愿

C．诚实信用

D．维护公共利益