Seeing them off at the airport_A.the foreign minister and other officials wereB.the foreign minister and other officialsC.was the foreign minister and other officialsD.were the foreign minister and other officials为什么选C不选D?

此句倒装句，主语是 the foreign minister and other officials，复数，所以用were。

26). Seeing them off at the airport were the foreign minister and other officials
.

到机场为他们送
行的有外长和其他官员。

应该是复数 形式D
你的答案有误

倒装
系动词单复数取决于系动词后面跟的名词的单复数形式,由于foreign minister是单数,所以用was
主语是the foreign minister and other officials,如果是正句就是:
the foreign minister and other officials were seeing them off at the airport
但倒过来是
seeing them off at the airport was the foreign minister and other officials.
为什么这样,跟你打个比方,就是某个大嘴播音员,不动脑子,看到什么说什么,看到就人在机场送行,就说seeing them off at the ariport,看到大领导,所以就was the foreign official,说着说着又忘了还有其它人,所以就补上and other officials.
注意从语法角度讲,the foreign minister and other officials不是一个主语,而是双主语,用and连接的词作主语,要看是双主语还是单主语,and前后是一个整体时,谓语用复数,如tom and baker are twins.当不是一个整体时就是双主语,谓语单复数取决于离系动语最近的一个主语.如the captain and his crew were fighting monsters.(the crew and the captain was fighting monsters.)