Final answer:
The entire adjective clause in the sentence is 'shame that so few people'. It modifies the noun 'shame' and describes what kind of shame it is.
Step-by-step explanation:
The entire adjective clause in the sentence is option c: 'shame that so few people.' It modifies the noun 'shame', describing what kind of shame it is. The word 'that' is a relative pronoun that introduces the adjective clause. The entire sentence can be understood as 'It's a shame that so few people attended the party.'