The correct answer is A. Insincere.
A specious argument is one that is superficially convincing but actually flawed. It may be based on false premises, misleading evidence, or logical fallacies. Insincere people are not honest or genuine. They may say things that they do not believe or pretend to be someone they are not.
The other options are not synonyms of specious.
B. Sharp is an adjective that means “keen,” “clever,” or “astute.” It can also mean “having a sharp edge or point.”
C. Straight is an adjective that means “not curved or bent.” It can also mean “honest,” “upright,” or “moral.”
D. Frank is an adjective that means “open and honest.” It can also mean “blunt” or “undiplomatic.”