Which of the following words is closest in meaning to “Dubious”?

Dubious means doubtful.

• Correct answer - doubtful: it has the same meaning as Dubious.
• external: outside - wrong, it does not mean the same as Dubious.
• straight: not bent - wrong, it does not mean the same as Dubious.
• sincere: genuine - wrong, it does not mean the same as Dubious.