Correct Answer: uncertain

Solution : The second option is the correct answer.

The word dubious refers to a state of uncertainty or scepticism, indicating a lack of confidence or reliability in a particular situation or piece of information. On the other hand, the synonym uncertain also embodies the concept of doubt and a lack of surety.

The meanings of the other options are as follows:

• Notable refers to being worthy of attention or remarkable.

• Impressive denotes evoking admiration or respect.

• Unwilling means not willing or reluctant.

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Therefore, the correct answer is uncertain.