Correct Answer: decisive

Solution : The fourth option is correct.

The underlined word irresolute in the sentence implies a lack of determination or firmness in making decisions. It describes individuals who are hesitant, indecisive, or uncertain. On the other hand, the antonym decisive refers to the ability to make decisions quickly and effectively, settling issues with confidence and determination.

The meanings of the other options are as follows:

• Harsh means severe or strict; unpleasantly rough or severe.
• Variant is a form or version that differs in some respect from other forms of the same thing.
• Default means failure to fulfil an obligation, pay a debt, or exercise a pre-selected option.

Therefore, the correct answer is decisive.