The correct option is
D
regret
The highlighted word means 'A feeling of regret'.
Option D is correct. As we can see, the option has the same meaning as the required one. Thus, it is the correct answer
Options A, B and C are incorrect. They do not have the required meaning.
'Confusion' means 'to not be able to think clearly'.
'Wonder' means 'to have a desire to know something'.
'Anger' means 'a strong feeling of displeasure'.