Which phrase in this excerpt from kurt vonneguts report on the barnhouse i s an example of sarcasm

The answer is: To ask how much longer the professor will live is to ask how much longer we must wait for the blessings of another world war.

Explanation:

The excerpt is:

To ask how much longer the professor will live is to ask how much longer we must wait for the blessings of another world war. He is of short-lived stock: his mother lived to be fifty-three, his father to be forty-nine; and the life-spans of his grandparents on both sides were of the same order. He might be expected live, then, for perhaps fifteen years more, if he can remain hidden from his enemies. When one considers the number and vigor of these enemies, however, fifteen years seems an extraordinary length of time, which might better be revised to fifteen days, hours, or minutes. The professor knows that he cannot live much longer. I say this because of the message left in my mailbox on Christmas Eve. Unsigned, typewritten on a soiled scrap of paper, the note consisted of ten sentences. The first nine of these, each a bewildering tangle of psychological jargonand references to obscure texts, made no sense to me at first reading. The tenth, unlike the rest, was simply constructed and contained no large words.

The answer therefore is:

To ask how much longer the professor will live is to ask how much longer we must wait for the blessings of another world war.

What makes it a sarcasm is the use of the word "blessings" to describe a war. This is because a world war is a bad situation and never brings blessings rather devastation.