A. As elephants trumpet, the high-frequency vibrations of their massive vocal chords reach the ears of other elephants within a mile.

B. This is especially useful in the jungle, where dense vegetation rapidly degrades auditory information, though not seismic cues.

C. A two-tiered communication model based on hearing and feeling provides an effective way of sending messages to nearby herd members as well as more distant rival herds.

D. Remarkably, the low frequencies travel through the ground to be picked up by the extremely sensitive feet of elephants up to six miles away.

A. Tatar was the common name for Turkic-speaking, semi-nomadic people living on or around the immense steppes of the Eurasian continent.

B. Duke Vytautas welcomed them. In return, the Tatars provided their new country, and later Poland, with military assistance against Tamerlane.

C. After the dissolution of the Mongol empire, a group of Muslim Tatars, fleeing the Turko-Mongol ruler Tamerlane, asked the Christian grand duke of Lithuania for asylum.

D. John III Sobieski, the king of the Polish-Lithuanian Commonwealth, might not have won the Battle of Vienna were it not for the help of his country’s Sunni Muslim Tatars.

A. The reader's mind naturally seeks to complete the shapes, and in doing so, it slows down the reading process and improves memory.

B. Based on this idea, a new font, Sans Forgetica, has been created by psychology and design researchers at RMIT University in Melbourne.

C. Sans Forgetica is sleek and back-slanted with intermittent gaps in each letter, which serve as a simple puzzle for the reader.

D. People remember things better when their brains have to overcome minor obstacles while processing information.

A. A drop in household consumption due to the rise in private debt was a key driver of the recession in the U.S.

B. Indeed, the lack of regulatory control over the growth in credit as well as the flow of credit into real estate was the issue.

C. A crucial aspect of the 2008 financial crisis was the build-up of debt in households and in non-financial firms.

D. This, however, is not to negate the view that regulatory failure was the principal cause of the crisis.

A. More recently, the concentration of a few dominant players in many industries, along with the decline of labor unions, has raised the issue of monopsony once again.

B. Monopsony power was a key feature of the company towns that helped define the Industrial Revolution, since everybody served one employer in most of these towns.

C. In the labor market context, this means that negotiating ability is tilted toward corporations, making it difficult for workers to push for higher pay.

D. Monopsony is a situation wherein there are many providers of a product in the market but only one dominant buyer, who holds all the cards and can drive prices down.