句1：I think it a good idea to be a singer and dancer.
主语：I
谓语：think
形式宾语：it
宾语补足语：a good idea
真正的宾语： to be a singer and dancer.
句2：I think it is a good idea to be a singer and dancer
主语：I
谓语：think
宾语（从句）： it is a good idea
宾语从句的形式主语：it
宾语从句真正的主语：to be a singer and dance