Step 1: Understand the meaning of ``Candid''.
The word ``candid'' means truthful, honest, and straightforward in speech or expression.
Step 2: Analyze the options.
Deceptive means misleading or dishonest, which is the opposite of candid.
Frank means open and honest, which matches the meaning of candid.
Secretive means hiding information.
Ambiguous means unclear or confusing.
Step 3: Conclusion.
Therefore, the correct synonym of ``candid'' is Frank.