Correct Answer: Hesitate

Solution : The fourth option is the correct answer.

Vacillate suggests a wavering or fluctuating between different options or opinions, reflecting an inability to make a firm decision, and hesitate specifically emphasises a momentary pause or reluctance to take action, often due to doubt, fear, or a lack of confidence.

The meanings of the other options are as follows:

• Advance means to move forward, progress, or promote.
• Stir means to mix or agitate, often with a utensil. Also to provoke or arouse.
• Plunge means to dive or fall suddenly and with force into something, such as water.