A. As that segment of ocean flow, known as the Gulf Stream, pushes north, it cools and becomes denser and eventually sinks, forming the so-called deepwater that flows back southward along the ocean floor toward Antarctica.

B. The warm, salty waters of the tropical Atlantic cruise northward along the eastern coast of the United States before darting toward northwestern Europe.

C. It also determines several climatic features, such as the latitude at which a key tropical rain belt is located, which impacts water supplies, precipitation for agriculture and the health of tropical ecosystems.

D. This cycle, called the Atlantic Meridional Overturning Circulation, plays a key role in moving heat around the planet as well as nutrients throughout the ocean.

A. These chemicals break an essential part of a bacterial cell, but they usually break the same part of human cells too.

B. This is the key to antibiotic function: exploiting the fact that bacteria are similar to human cells without being identical.

C. This makes medical antiseptics terrible antibiotics, as their use in high concentrations may cause tissue damage or slow wound healing.

D. Luckily, sometimes there are bacterial parts not found in humans, or if they are, they are very different.

E. It’s relatively easy to find new antiseptics, which can kill microbes on the skin and the surface of tissues.

A. But when it feels other ants walking on its back, the ant simply stays put.

B. When an ant on the march comes to a gap in its path, it slows down.

C. In this way, the ants build a bridge long enough to span whatever gap is in front of them.

D. The process repeats as the next ant in line slows, gets trampled and freezes in place.

E. The rest of the colony, still barreling along at 12 centimeters per second, comes trampling over its back.

A. With his iconic painting, Margritte showed how art can change our view of this world and give us a fresh opportunity to attempt to define the indefinable.

B. Magritte, who considered himself a thinker who communicated through paint, wanted to prove that images could equal words in the expression of consciousness.

C. In painting this, Margritte was inspired by the definition of a poem by popular literary figures André Breton and Paul Éluard, who declared that “Poetry is a pipe”.

D. One of René Magritte’s most famous paintings, “The Treachery of Images,” features an image of a tobacco pipe with the words “This is not a pipe” underneath it.

A. Hopelessness, exhaustion and dwindling control over national economic life are the themes of politics all across the world.

B. As a result, states have been forced to shed social commitments in order to reinvent themselves as custodians of the market.

C. This has drastically diminished national political authority in both real and symbolic ways.

D. The destruction of state authority over capital has been the clear-cut objective of the financial revolution that defines our present era.