你这里提到的是与think相关的两个句型:一个是think+宾语从句,相关表达就是Do you think (that) it is(缩略形式为it's) necessary to learn to wait in line?引导宾语从句的that可以省略,宾语从句有形式主语it,谓语is;一个是think +宾语+宾补(形容词),也就是你提供的句子Do you think it necessary to learn to wait in line?形式宾语为it,形容词necessary做宾补——不像宾语从句里有谓语。