Correct Answer: Careful

Solution : The correct choice is the third option .

Fastidiuous is someone who is very concerned about accuracy and detail. Careful is someone who is very attentive and cautious. Thus, it is the appropriate synonym.

The meanings of the other options are as follows:

• Hardworking is someone who puts a lot of effort into their work.
• Careless means not giving sufficient attention.
• Fast means moving at high speeds.

Therefore, the correct answer is careful.