choices.label: A B C D
choices.text: limit:constant steamship:ship simple equations:linear equations good offices:conciliation
explanation: "ultrasonic" is a kind of "mechanical wave". "limit" and "constant" are both mathematical terms, and "limit" is not a "constant". a "steamship" is a kind of "ship". the "simple equation" and the "linear equation" both belong to the same category. a "simple equation" is not a "linear equation". both "good offices" and "conciliation" refer to breaking a deadlock. the two are similar in their meanings, but "good offices" is not a kind of "conciliation".
relation: ultrasound mechanical waves R2.2
relation: limit constant R2.4
relation: steamship ship R2.2
relation: simple equations linear equations R2.1
relation: good offices conciliation R1.1