Answer:
B) evidence
Step-by-step explanation:
-Authority means the power someone has to make decisions or give orders.
-Evidence refers to proofs that demonstrate that something is true.
-Legality means that something is according to the law.
-Levity means that something is not treated with the necessary importance that it should be given.
According to the definitions, the answer is that when Kennedy uses the word substance he means evidence because he is trying to say that he doesn't have any proof that demonstrates that the speculations are true.