This offer has come as a great boon to me.

The correct answer is A. misfortune.

A boon is a blessing or advantage. A misfortune is an unlucky event or circumstance. A blemish is a small mark or defect that spoils the appearance of something. A curse is a solemn utterance intended to invoke a curse upon someone or something. Trouble is a state of difficulty or worry.

In the sentence “This offer has come as a great boon to me,” the word “boon” is used to mean “a blessing or advantage.” The offer is something that the speaker is happy about and that will help them in some way. The other options are all negative words that do not fit the meaning of the sentence.