A. Studies reveal that Martian brines today could hold higher concentrations of oxygen than were present on Earth about 2.4 billion years ago, when the first landmass emerged on Earth.

B. Although Mars is today a freeze-dried desert, it possesses abundant reserves of subsurface water ice, as well as some amount of liquid water in the form of brines.

C. These pools of salty liquid can capture even meager amounts of oxygen from the Mars’ atmosphere, creating a reservoir that microbes might metabolically utilize.

D. The brines’ high salt content lowers the temperature at which they freeze, allowing them to remain liquid even on the Red Planet's frigid surface.

A. In 17th-century Amsterdam, it was highly common for the guilds to commission portraits of themselves wearing their uniforms and holding weapons.

B. It was Rembrandt’s riveting interplay of light, motion, texture and expression transformed a commonplace commission into a masterwork.

C. Its status and critical acclaim, though, have little to do with its subject matter: a civic-guard group tasked with keeping watch on the city walls.

D. The painting Militia Company of District II Under the Command of Captain Frans Banninck Cocq, better-known as The Night Watch, is probably Rembrandt’s most famous work.

A. When the perceived cost of losing is sufficiently high, politicians may be tempted to abandon forbearance and play constitutional hardball.

B. When parties view one another as mortal enemies, the stakes of political competition heighten dramatically.

C. Such behavior, in turn, might further undermine mutual toleration, reinforcing the false belief that political rivals pose a dangerous threat.

D. Losing ceases to be a routine and accepted part of the political process and instead becomes a full-blown catastrophe.

A. The quest to define units of measurement using constants of nature goes back to the creation of the metric system during the French Revolution.

B. It was a utopian project, with its creators imagining that a shared system of weights and measures would unite the world, allowing for the free exchange of goods and information.

C. The metric system was created with the intention of liberating the common man and woman from the confusing and inconsistent weights and measures of the old regime.

D. At this time, the ideology of liberty, equality, fraternity was embraced not just by revolutionaries, but by scientists as well.

Each passage consist of six sentences. The first and sixth sentence are given in the begining. The middle four sentences in each have been removed and jumbled up. These are labelled as P, Q, R and S. Find out the proper order for the four sentences.

S1: The future beckons to us.
P: In fact we have hard work ahead.
Q : Where do we go and what shall be our endeavour?
R : We shall also have to fight and end poverty, ignorance and disease.
S : It will be to bring freedom and oppurtunity to the common man.
S6: There is no resting for any one of us till we redeem our pledge in full.

The Proper sequence should be: