2 . The Hope Diamond is one of the world’s most famous jewels. It was in the possession of a series of people: kings, bankers, rich women and thieves, before its arrival 60 years ago at the Smithsonian Institution in Washington, D.C.

As a rare blue diamond, it has a complex social history, to be sure. But, far more so is its geological history, researchers say in a new report. This is the first time anyone has come up with a fact-based study or model for how blue diamonds form.

The group looked at 42 blue diamonds, including one from South Africa that recently sold for $25 million in 2016. Researchers could tell where the stones were formed based on the very small minerals trapped inside.

Diamonds are a hard, clear form of pure carbon called a crystal (结晶). They form under extreme heat and pressure. Blue diamonds crystallize alongside water-bearing minerals that long ago were part of the floor of the sea. But these minerals were pushed deeper underground during the movement of the Earth’s plates.

Scientists already knew these diamonds received their blue color from the element boron (硼). The study says that boron had once been in ocean water but was eventually pushed into the seafloor rock. Over millions of years, the boron continued to move deep underground.

Many diamonds appear colorless. Often, however, they have some yellow color. Still others have a light brown, pink or green color. About 99 percent of all diamonds form somewhere between 150 to 200 kilometers underground, a far shallower birthplace than their blue relations. “These diamonds are among the deepest ever found,” Carnegie Institution for Science geochemist Steven Shirey said of the blue diamonds.

The public can see the Hope Diamond at the Smithsonian National Museum of Natural History in Washington D.C.

1. By saying the underlined part in Paragraph 2, the researchers mean the blue diamond ________.

A．was formed in extreme weather

B．has a very complex forming history

C．has a far-reaching influence in society

D．used to be very popular among rich people

2. How could researchers know the blue diamonds’ birthplaces?

A．By observing their colors.

B．By studying their structures.

C．By referring to where they were found.

D．By examining tiny substances in them.

3. What makes the diamonds appear blue?

A．The water.	B．Extreme heat and pressure.
C．A special matter.	D．The seafloor rock.

4. What is special about blue diamonds compared with diamonds of other colors?

A．They contain several colors.

B．They form in much deeper underground.

C．They come into being in a different way.

D．They are found near the earth’s surface.

5. What is the passage mainly about?

A．The social status of the Hope Diamond.

B．The discovery of the Hope Diamond.

C．The formation of the blue diamond.

D．The diversity of diamonds.