Answer:
B. By putting quotation marks around a phrase
Step-by-step explanation:
The author places quotation marks around the sentences to show the opposite meaning between the two sentences and the confusion about which phrase to follow. This happens in the text in the following part: "we may be tempted to try to live by the Christian ideal of being "our brother's keeper," or by the Marxist ideal of "to each according to his needs."
The author shows that there is an opposition between "our brother's keeper" and "to each according to his needs". They are phrases that do not match and that have different purposes.