Final answer:
In the sentence given, the noun clause is ' Whoever believes what Roberta said', as it serves as the subject by performing the action of the sentence. Option a is correct.
Step-by-step explanation:
The noun clause in the sentence 'Whoever believes what Roberta said should stand by her' is 'a. Whoever believes what Roberta said'.
A noun clause is a dependent clause that acts as a noun. In this sentence, the noun clause is the subject of the sentence, as it is the thing performing the action of 'standing by' Roberta.
Therefore, option a ('Whoever believes what Roberta said') serves as the subject of the sentence and comprises the noun clause.
Hence, In the sentence given, the noun clause is ' Whoever believes what Roberta said', as it serves as the subject by performing the action of the sentence. Option a is correct.